When I switch from Opera 26 to another window, Opera pops up its home menu over my next Window.

I just realized - while writing this post - that the problem appears when ALT is pressed slightly before TAB.
That makes the Opera home menu pop up. So that's bad by itself.

Then when when you switch to the other window, the home menu of Opera remains positioned above the new window.

Version:	26.0.1656.60 - Opera is up to date
Update stream:	Stable
System:	Windows 7 64-bit (WoW64)