Created Unassigned: Focusing issue when having floating documents [16251]

When having a floating document which is in focus and clicking on a menu item in the main window (or any other control not in a document or acnhorable) the focus is not set correctly.

Steps to reproduce:

- Run MVVMTestApp
- Open two documents
- Float one of them
- __Click on the "Tools" menu, and it opens correctly.__
- Now, click inside the _docked_ document (focusing its TextBox)
- Click on the floating document
- __Click on the "Tools" menu, and it does not open__ instead focus is set to the TextBox inside the docked document.