you are not notified...........you have to notice it yourself, when you look at your own questions list, and you can plainly see that the category has been changed.
for instance......I just asked a question about "dirty pool" on P&S, and within minutes, some idiot changed it to Global Warming.
minutes after that, it was switched to Yahoo Answers.
I've had single questions switched over 20 times. ...bouncing from category to category.
I can Always move it back easily enough, being level 7 myself, plus , it's MY question...........but I let the trolls have their fun.