I had this in P7 for Mac on a single sided plane I was using for a mirror. Having rotated it 90 degrees around the x-axis to stand it on end, I could no longer rotate it around the y-axis. The y-rotation dial did the same as the z-rotation dial, just as in your example.

Sorry, I didn't get to the bottom of the problem, but I need to bookmark this thread to see what others have to say about it.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)