diff --git a/LDK/resources/web/LDK/plugin/UserEditableCombo.js b/LDK/resources/web/LDK/plugin/UserEditableCombo.js
index c3ce9a2d..a4455866 100644
--- a/LDK/resources/web/LDK/plugin/UserEditableCombo.js
+++ b/LDK/resources/web/LDK/plugin/UserEditableCombo.js
@@ -12,6 +12,7 @@ Ext4.define('LDK.plugin.UserEditableCombo', {
 
     alias: 'plugin.ldk-usereditablecombo',
     allowChooseOther: true,
+    useBracketsForUnknownValues: false,
 
     init: function(combo) {
         this.combo = combo;
@@ -84,6 +85,7 @@ Ext4.define('LDK.plugin.UserEditableCombo', {
                 var rec = this.store.createModel({});
                 rec.set(this.valueField, val);
                 rec.set(this.displayField, val);
+                rec.set("invalid", true);
 
                 this.store.add(rec);
             },
@@ -95,6 +97,47 @@ Ext4.define('LDK.plugin.UserEditableCombo', {
             }
         });
 
+        if (this.useBracketsForUnknownValues) {
+            let innerTpl = 'this.formatLookup(values)';
+
+            const innerTplWrap = this.combo?.listConfig?.getInnerTpl();
+            if (typeof innerTplWrap === 'string') {
+                innerTpl = innerTplWrap.replaceAll('values', innerTpl);
+            }
+            else if (Array.isArray(innerTplWrap)) {
+                innerTpl = innerTplWrap.map(t => t.replaceAll('values', innerTpl));
+            }
+            else {
+                innerTpl = '{[' + innerTpl + ']}';
+            }
+
+            Ext4.override(combo, {
+                tpl: Ext4.create('Ext.XTemplate',
+                    '<ul class="x4-list-plain">',
+                        '<tpl for=".">',
+                            '<li role="option" class="x4-boundlist-item">',
+                                '' + innerTpl,
+                            '</li>',
+                        '</tpl>',
+                    '</ul>',
+                    {
+                        formatLookup: function(value) {
+                            const val = value[this.field.displayField] || value[this.field.valueField] || '';
+                            if (Ext4.isEmpty(val)) {
+                                return '';
+                            }
+
+                            if (value.invalid) {
+                                return '[' + LABKEY.Utils.encodeHtml(val) + ']';
+                            }
+
+                            return LABKEY.Utils.encodeHtml(val);
+                        }
+                    }
+                )
+            });
+        }
+
         combo.store.on('add', this.onStoreAdd, this);
         combo.store.on('load', combo.ensureValueInStore, combo);
         combo.store.on('beforerender', combo.ensureValueInStore, combo);