fix hiding of "Add" input on comboboxes with fixed options

the check for this needs to be done after the available options are actually refreshed

CHANGELOG.md

@@ -44,6 +44,7 @@ _Breaking developer changes, which may affect downstream projects or sites that
 #### :white_check_mark: Validation
 #### :bug: Bugfixes
 * Fix `multi/many/semiCombo` options for not being selectable immediately after removing them for fields with predefined options
+* Fix a bug where the _Add_ input element on comboboxes with a fixed set of allowed options is still hidden after an option of a previously "fully saturated" field is removed
 #### :earth_asia: Localization
 * Send `Accept-Language` header on Nominatim API calls ([#9501], thanks [@k-yle])
 * Add Address and Phone Format for India ([#9482], thanks [@biswajit-k])

modules/ui/fields/combo.js

@@ -325,6 +325,12 @@ export function uiFieldCombo(field, context) {
 
         _container.selectAll('input')
             .attr('placeholder', ph);
+
+        // Hide 'Add' button if this field uses fixed set of
+        // options and they're all currently used
+        var hideAdd = (!_allowCustomValues && !values.length);
+        _container.selectAll('.chiplist .input-wrap')
+            .style('display', hideAdd ? 'none' : null);
     }
 
 
@@ -610,20 +616,13 @@ export function uiFieldCombo(field, context) {
             // a negative maxlength doesn't make sense
             maxLength = Math.max(0, maxLength);
 
-            var allowDragAndDrop = _isSemi // only semiCombo values are ordered
-                && !Array.isArray(tags[field.key]);
-
-            // Exclude existing multikeys from combo options..
-            var available = objectDifference(_comboData, _multiData);
-            _combobox.data(available);
-
-            // Hide 'Add' button if this field uses fixed set of
-            // options and they're all currently used,
-            // or if the field is already at its character limit
-            var hideAdd = (!_allowCustomValues && !available.length) || maxLength <= 0;
+            // Hide 'Add' button if this field is already at its character limit
+            var hideAdd = maxLength <= 0;
             _container.selectAll('.chiplist .input-wrap')
                 .style('display', hideAdd ? 'none' : null);
 
+            var allowDragAndDrop = _isSemi // only semiCombo values are ordered
+                && !Array.isArray(tags[field.key]);
 
             // Render chips
             var chips = _container.selectAll('.chip')