Can not create multi level menus on the Channel Manager UI

Reproduction steps:
0. Have a menu which has a property level set to at least 2.
1. Open the CMS.
2. Open the channel manager in edit mode.
3. Edit the above menu.
4. Try to create a new submenu item inside one menu item.

Expected result:
I can create it.

Actual result:
I can not. I need to go to the console and move by hand the submenu item to the desired place.