TYPO3 Core

Steps to reproduce:

1. Set target as required: $GLOBALS['TCA']['pages']['columns']['target']['config']['eval'] = 'trim,required';
2. Create new page of Type "Link to external URL [3]"
3. Select a target with the value picker

Expected : onChange triggers validation of the field and the form can be submitted
Actual : No validation is triggered and the form can not be submitted due to mandatory fields being "empty"

In v10 the fieldChangeFunc is added to the onclick attribute: TBE_EDITOR.fieldChanged(...);
In v11 the fieldChangeFunc is empty and therefore nothing happens when selecting a value via the value picker.

Side note: You can also test this in the Site Configuration module by adding a new language and selecting the Locale via the value picker.