If it bothers you (which, presumably, it does - at least enough to post here about it), then I'd have a quiet word with the DM after the game. Preferably one-to-one, and preferably face-to-face. It's entirely possible it was a simple oversight on his behalf, in which case having the quiet word is no bad thing. Equally, it's entirely possible he deliberately made that change, in which case he'll no doubt tell you. Either way, it shouldn't be a problem, provided you address it with tact and maturity.
If, after you've spoken to the DM, it continues to really bug you, such that you're no longer enjoying the game, then you should drop out and let the rest of the group have their fun without you. That's obviously an extreme step, but life's too short to play in a game you're not enjoying, but you also shouldn't prevent others from playing games that they are.