What is causing Photoshop to always stay on top? I'm on Mac OS X El Cap. And I'm using PS CS 6 Extended.

If I switch to Photoshop, and do my work, then try to switch to say Chrome via cmd+tab, Photoshop stays on top.

My questions:


What might have caused this? Did I accidently click something on my Mac that makes Photoshop float?
How can I fix this problem to have PS behave like any other app in terms of visibility.
It's not a complete fix, but I have found that if I click on Chrome in the dock instead of switching via the keyboard, then it does let Chrome be on top.