I've been thinking some more about this, and my suspicion that language/region is at the heart of it grows.
It has to be, because most regulars here claim they have never seen it. I suspect most of them have English application, OS and keyboard. No conflicting languages.
But I have noticed this annoying little thing pop up for years. Eight or ten Photoshop versions back (at least), five or six different machines in different environments, with different OS'es from Vista to 10. The only thing I can think of that they all have in common, is English Photoshop, English OS - but Norwegian keyboard layout and input. Keyboard input language is a separate variable in Windows, independent from main language.
Once in a blue moon the keyboard setting switches by itself from Norwegian to English. Then the Photoshop shortcuts go completely crazy, so I notice right away. In that case they still work, but zoom in suddenly becomes zoom out, and so on.