Items are not checked in View menu with stacked dockwidgets

(Feel free to edit the title, I'm not sure how to put it well)
commit: 02d03c9
OS: Windows 10
Steps:
1) Open timeline
2) Open piano keyboard
3) Drag the piano keyboard onto the timeline to create tabs
4) Look in the View menu

Result:
The top level dock widget is checked, but not the one under it.

Desired:
All currently open widgets are checked in the view menu, regardless of position or tab location.

This can also be recreated with the text editor by adding staff text and double clicking the text, dragging the timeline/piano keyboard onto the text entry, and putting the text entry on top. Similar steps can be taken for the drum entry for the same bug.