Steps to reproduce the issue

• I have several site menus. See image (green arrows).

• Edit a module > Tabulator "Menu Assignment".
• Set Module Assignment: "On the pages selected".
• Click Assign to Menu Items: "None", to deselect all items.
• Click button to select/deselect sub-items of a menu and click on "Select" See image (orange arrow).

Expected result

• Only sub-items of relevant menu are selected (here "Bibliografie").

Actual result

• All sub-items of other menus are also selected. See image (red comments).

System information (as much as possible)

• Joomla 4, current nightly, 30 October 2020 02:00:25 UTC.
• XAMPP7.3, Windows 10
• Current Edge chromium, current FF

Additional comments

• Similiar behavior inside the same menu with select feature used for sublevels. See image (red comment).