diff --git a/crates/engine/src/cmd/data.rs b/crates/engine/src/cmd/data.rs
index 383624b70..28e4060fe 100644
--- a/crates/engine/src/cmd/data.rs
+++ b/crates/engine/src/cmd/data.rs
@@ -1199,7 +1199,7 @@ fn detail(s: &mut Session, p: &Json, hide: bool) -> Result<Json> {
                 .collect();
             for i in g.start..=g.end {
                 if let Some(e) = map.get_mut(&i) {
-                    e.hidden = hide || inner.iter().any(|o| o.contains(i));
+                    set_hidden(e, hide || inner.iter().any(|o| o.contains(i)));
                 }
             }
             if hide {
@@ -1213,6 +1213,16 @@ fn detail(s: &mut Session, p: &Json, hide: bool) -> Result<Json> {
     })
 }
 
+/// Hides or shows an outline line. A line shown with a zero size (files that hide columns as
+/// `width="0" hidden="1"`) gets the default size back, as Unhide does; otherwise + would mark the
+/// group expanded and leave it invisible (#1714).
+fn set_hidden(e: &mut LineInfo, hidden: bool) {
+    e.hidden = hidden;
+    if !hidden && e.size == Some(0.0) {
+        e.size = None;
+    }
+}
+
 /// The outline's level buttons: show rows / columns down to outline level `n` (1 = only the
 /// top-level summaries); deeper detail is hidden and its summary lines marked collapsed.
 fn show_levels(s: &mut Session, p: &Json) -> Result<Json> {
@@ -1231,7 +1241,7 @@ fn show_levels(s: &mut Session, p: &Json) -> Result<Json> {
             let Some(n) = n else { continue };
             let groups = outline::groups(map);
             for e in map.values_mut().filter(|e| e.outline > 0) {
-                e.hidden = e.outline >= n;
+                set_hidden(e, e.outline >= n);
             }
             // Inner groups come first, so a summary line shared with the group around it ends up
             // as that outer group says.
@@ -1367,6 +1377,31 @@ mod tests {
         assert!(!ok(&mut s, "B1", "150"));
     }
 
+    #[test]
+    fn showing_detail_gives_zero_width_columns_their_width_back() {
+        // #1714: templates hide grouped columns as `width="0" hidden="1"`; + must show them.
+        let mut s = Session::new();
+        s.new_workbook();
+        let hidden = LineInfo { size: Some(0.0), hidden: true, outline: 1, ..LineInfo::default() };
+        let sh = Arc::make_mut(&mut s.doc_mut().unwrap().wb).sheet_mut(0).unwrap();
+        for c in 2..=4 {
+            sh.cols.insert(c, hidden);
+        }
+        sh.cols.insert(5, LineInfo { collapsed: true, ..LineInfo::default() });
+        s.execute("data.showDetail", json!({"cols": "C:E", "level": 1})).unwrap();
+        let sh = s.doc().unwrap().wb.active().unwrap();
+        for c in 2..=4 {
+            assert_eq!(sh.col_width(c), sh.default_col_width, "column {c}");
+        }
+        // Hiding again hides them; the level buttons show zero-width columns too.
+        s.execute("data.hideDetail", json!({"cols": "C:E", "level": 1})).unwrap();
+        assert_eq!(s.doc().unwrap().wb.active().unwrap().col_width(2), 0.0);
+        Arc::make_mut(&mut s.doc_mut().unwrap().wb).sheet_mut(0).unwrap().cols.insert(3, hidden);
+        s.execute("data.showLevels", json!({"cols": 2})).unwrap();
+        let sh = s.doc().unwrap().wb.active().unwrap();
+        assert_eq!((sh.col_width(2), sh.col_width(3)), (sh.default_col_width, sh.default_col_width));
+    }
+
     #[test]
     fn removing_an_autofilter_keeps_manually_hidden_and_collapsed_rows() {
         let mut s = Session::new();