Honestly, unless the GM can come up with a good excuse, I think keeping players from knowing when their spells succeed/fail is a bad play on the side of a GM. It just detracts from the game play over all, "foul play" if you will. Also it's sort of like common sense. There are several feats and things, and a good example is the "once per day" abilities that exist everywhere. If it can only affect a target once per day, how is the player suppose to know?
I'm trying really hard not to bluntly say, any GM that does this is a jerk, but really..come on guys. This game is designed to have fun, not cause people to get upset.
Sometimes people may get this confused. This does -not- mean the player is entitled to know WHY their ability failed, only that it failed.