diff --git a/crates/calc/src/eval/call.rs b/crates/calc/src/eval/call.rs
index 848762ab9..fe185e700 100644
--- a/crates/calc/src/eval/call.rs
+++ b/crates/calc/src/eval/call.rs
@@ -52,13 +52,16 @@ impl<'h> Evaluator<'h> {
             "ISFORMULA" | "FORMULATEXT" => {
                 let Some(Ev::R(a)) = args.first().map(|a| self.eval(a)) else { return err(CellError::NA) };
                 let Some(a) = a.first() else { return err(CellError::NA) };
-                let f = self.host.workbook().sheet(a.sheet).and_then(|s| s.cell(a.range.start)).and_then(|c| c.formula.clone());
+                let wb = self.host.workbook();
+                let f = wb.sheet(a.sheet).and_then(|s| s.cell(a.range.start)).and_then(|c| c.formula.clone());
+                // A formula formatted Hidden on a protected sheet stays hidden from FORMULATEXT too.
+                let hidden = wb.sheet(a.sheet).is_some_and(|s| s.is_protected() && wb.styles.get(s.style_id(a.range.start)).protection.hidden);
                 if name == "ISFORMULA" {
                     Ev::V(Value::Bool(f.is_some()))
                 } else {
                     match f {
-                        Some(f) => Ev::V(Value::text(format!("={}", f.text))),
-                        None => err(CellError::NA),
+                        Some(f) if !hidden => Ev::V(Value::text(format!("={}", f.text))),
+                        _ => err(CellError::NA),
                     }
                 }
             }
diff --git a/crates/engine/src/cmd.rs b/crates/engine/src/cmd.rs
index da130fe2a..a59bf9b2a 100644
--- a/crates/engine/src/cmd.rs
+++ b/crates/engine/src/cmd.rs
@@ -366,6 +366,10 @@ pub struct Ctx<'a> {
     pub wb: Workbook,
     pub changed: Vec<Key>,
     pub structural: bool,
+    /// Recalculate every formula without the other effects of `structural` (table headers are not
+    /// resynchronized, array formulas are still checked): for edits that change only what a
+    /// function reads, like sheet protection.
+    pub recalc_all: bool,
     pub sel: &'a mut Selection,
     /// Rows whose automatic height should be recomputed (sheet, row).
     pub fit_rows: Vec<(usize, u32)>,
@@ -400,13 +404,14 @@ pub(crate) fn commit<R>(d: &mut DocState, f: impl FnOnce(&mut Ctx) -> Result<R>)
         wb: (*d.wb).clone(),
         changed: Vec::new(),
         structural: false,
+        recalc_all: false,
         sel: &mut sel,
         fit_rows: Vec::new(),
         protection_checked: false,
         edits: Vec::new(),
     };
     let r = f(&mut ctx)?;
-    let Ctx { mut wb, mut changed, structural, mut fit_rows, protection_checked, edits, .. } = ctx;
+    let Ctx { mut wb, mut changed, structural, recalc_all, mut fit_rows, protection_checked, edits, .. } = ctx;
     // Equations whose source changed (or that arrived without a layout, as from a paste) are
     // laid out here, so painting only ever reads the cache.
     wb.refresh_equations();
@@ -435,7 +440,7 @@ pub(crate) fn commit<R>(d: &mut DocState, f: impl FnOnce(&mut Ctx) -> Result<R>)
     if let Some(t0) = t0 {
         eprintln!("commit: edit {:?}, {} changed", since(t0), changed.len());
     }
-    if structural {
+    if structural || recalc_all {
         d.calc.recalc_all(&mut wb);
     } else if !changed.is_empty() {
         d.calc.cells_changed(&mut wb, &changed);
diff --git a/crates/engine/src/cmd/review.rs b/crates/engine/src/cmd/review.rs
index de9c98ecd..7eafa26db 100644
--- a/crates/engine/src/cmd/review.rs
+++ b/crates/engine/src/cmd/review.rs
@@ -163,6 +163,8 @@ fn protect_sheet(s: &mut Session, p: &Json) -> Result<Json> {
     let what = d.wb.sheet(sheet).map(|sh| sh.name.clone()).unwrap_or_default();
     let prot = SheetProtection { password: str_param(p, "password").filter(|x| !x.is_empty()).map(|pw| new_password_hash(d, &what, pw)), ..prot };
     edit(s, |cx| {
+        // FORMULATEXT reads a sheet's protection: its results are recalculated.
+        cx.recalc_all = true;
         cx.sheet_mut(sheet)?.protection = Some(prot.clone());
         Ok(Json::Null)
     })
@@ -182,7 +184,10 @@ fn unprotect_sheet(s: &mut Session, p: &Json) -> Result<Json> {
         }
     }
     edit(s, |cx| {
-        cx.sheet_mut(sheet)?.protection = None;
+        // Only removing protection changes what FORMULATEXT reads; a no-op unprotect skips the full recalculation.
+        if cx.sheet_mut(sheet)?.protection.take().is_some() {
+            cx.recalc_all = true;
+        }
         Ok(Json::Null)
     })
 }
@@ -404,6 +409,21 @@ mod tests {
         assert_eq!(at(&s), (0, "A1".to_string()));
     }
 
+    #[test]
+    fn protecting_and_unprotecting_leave_table_headers_alone() {
+        let mut s = Session::new();
+        s.new_workbook();
+        s.execute("range.setValues", json!({"range": "A1", "values": [["a", "b"], [1, 2]]})).unwrap();
+        s.execute("insert.table", json!({"range": "A1:B2", "header": true})).unwrap();
+        // An imported header can hold a number: only a structural edit would turn it back into text.
+        let d = s.doc_mut().unwrap();
+        std::sync::Arc::make_mut(&mut d.wb).sheet_mut(0).unwrap().set_value(gridcraft_core::CellRef::new(0, 0), gridcraft_core::Value::Number(7.0));
+        s.execute("review.protectSheet", json!({})).unwrap();
+        s.execute("review.unprotectSheet", json!({})).unwrap();
+        let v = s.doc().unwrap().wb.sheet(0).unwrap().value(gridcraft_core::CellRef::new(0, 0));
+        assert_eq!(v, gridcraft_core::Value::Number(7.0));
+    }
+
     #[test]
     fn protection_that_forbids_selecting_locked_cells_is_enforced_and_kept() {
         let mut s = book();
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index ed5e33945..55e795a01 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -6480,6 +6480,23 @@ fn clearing_links_and_notes_keeps_allow_edit_ranges() {
     assert!(sh.hyperlinks.is_empty() && sh.comments.is_empty());
 }
 
+#[test]
+fn formulatext_does_not_reveal_a_hidden_formula() {
+    let mut s = s();
+    s.execute("cell.set", json!({"cell": "A1", "input": "=1+1"})).unwrap();
+    s.execute("home.formatCells", json!({"range": "A1", "style": {"protection": {"locked": false, "hidden": true}}})).unwrap();
+    s.execute("home.formatCells", json!({"range": "B1", "style": {"protection": {"locked": false}}})).unwrap();
+    s.execute("cell.set", json!({"cell": "B1", "input": "=FORMULATEXT(A1)"})).unwrap();
+    assert_eq!(v(&s, "B1"), Value::from("=1+1"), "not protected yet");
+    s.execute("review.protectSheet", json!({})).unwrap();
+    // Without entering the formula again: protecting recalculates what reads the protection.
+    assert_eq!(v(&s, "B1"), Value::Error(gridcraft_core::CellError::NA));
+    s.execute("cell.set", json!({"cell": "B1", "input": "=FORMULATEXT(A1)"})).unwrap();
+    assert_eq!(v(&s, "B1"), Value::Error(gridcraft_core::CellError::NA));
+    s.execute("review.unprotectSheet", json!({})).unwrap();
+    assert_eq!(v(&s, "B1"), Value::from("=1+1"), "unprotecting shows it again without re-entering");
+}
+
 #[test]
 fn protected_sheet_refuses_layout_commands_its_permissions_do_not_allow() {
     let mut s = s();
diff --git a/crates/ui-egui/src/app/editing.rs b/crates/ui-egui/src/app/editing.rs
index 8682a435c..a5ac8a176 100644
--- a/crates/ui-egui/src/app/editing.rs
+++ b/crates/ui-egui/src/app/editing.rs
@@ -50,6 +50,11 @@ impl SheetApp {
             self.session.mode = gridcraft_engine::Mode::Edit;
             return;
         }
+        // A hidden formula's source isn't loaded into an edit (a blank edit would also write over
+        // it on commit): no edit starts. Typing still replaces the cell.
+        if text.is_none() && gridcraft_engine::display::formula_hidden(&d.wb, sh, at) {
+            return;
+        }
         let locale = self.ui.language.formula_locale();
         let current = if sh.cell_pictures.contains_key(&at) {
             String::new()