Quite simple.

Redstone torches fall off every time the block it is resting on gets powered. They will only stay on when the block is not powered. I find it odd, because I was working in this same map having no problems about 45 minutes before, and then I got back on and I tried to make essentially a pulse shortener and i couldn't place the torch on a powered block. I then tried to see if this was only for this particular map and I loaded up another map and it continued to do the same. I cannot place a torch on a powered block. And any block that gets powered, the redstone torch will fall off.