Alt+Tab behaves strangely

Hello.
Not sure what to call the thread. The problem is kinda unique.. but here's the issue:

I have the following windows open at the moment:
Diablo 3 (running in background)
Battle.net (was last in focus)
Malwarebytes (searching for viruses)
Google Chrome (in focus, writing this post)

If I press Alt+Tab (AT) quickly I expect have the program Battle.net in focus (since it was last in focus). -This works just fine. No problem.
If I AT to Diablo 3, from Google Chrome - and then want to AT once more I expect to go back to Google Chrome (since it was last in focus) - and this also works as expected, still no problem.
But here's the problem:
If I press AT again I expect to go back into Diablo 3. But suddenly my computer seems to be confused and think that Battle.net was last in focus (which it wasn't), and pressing AT will put Battle.net in focus. -When it really should've been Diablo 3.

So in short: Alt+Tabbing out of Diablo 3 seems to confuse my computer, and mess up the order of which window was last in focus. (I can't AT out of Diablo 3 and then AT back into it.)

I haven't tried right now, but I believe that I have the same issue in other games as well. Not sure if the issue is dependant on Diablo 3 or not.

I used to use Windows 8, and I didn't have this issue in Win8. -I could AT in and out of games no problem.

Check for malware, test System files, establish a Clean Boot, utilize System Resources to check for Problems/Solutions, resolve repeat errors from Troubleshooting Steps for Windows 7.

Report back as you go as other steps may be indicated.