removed dependency on option list of custom option

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## [`master`](https://github.com/elastic/eui/tree/master)
 
+- Removed dependency on option list for custom option of `EuiComboBox` ([#3183](https://github.com/elastic/eui/pull/3183))
 - Fixed `EuiPopover` arrow position in Android and Linux ([#3188](https://github.com/elastic/eui/pull/3188))
 - Improved `htmlIdGenerator` when supplying both `prefix` and `suffix` ([#3076](https://github.com/elastic/eui/pull/3076))
 - Updated pagination prop descriptions for `EuiInMemoryTable` ([#3142](https://github.com/elastic/eui/pull/3142))

src/components/combo_box/combo_box.tsx

@@ -472,7 +472,18 @@ export class EuiComboBox<T> extends Component<
     if (async) {
       return false;
     }
-    return flattenOptionGroups(options).length === selectedOptions.length;
+    let numberOfSelectedOptions = 0;
+    selectedOptions.forEach(({ label }) => {
+      if (
+        flattenOptionGroups(options).findIndex(
+          option =>
+            option.label.trim().toLowerCase() === label.trim().toLowerCase()
+        ) !== -1
+      )
+        numberOfSelectedOptions += 1;
+    });
+
+    return flattenOptionGroups(options).length === numberOfSelectedOptions;
   };
 
   isSingleSelectionCustomOption = () => {