similar thing inda happened to me, except that my key couldn´t turn my ignition, but could still turn every other lock. the ignition was just plain worn out inside, as was the key. it was just a no go anymore, and before long the rest of my locks will have to go too. not the cheapest thing to fix, especially if you take it in, and taking apart your whole dash / steering column n stuff (maybe it´s easier than that to replace the ignition switch) can be dicey if you´re not sure what to do. i took mine in unfortunatly, and they only replaced the ignition, gave me a new key, and gave me new locks for the doors / hatch separatly at no extra charge 
so it could be plain worn out, and a sign that the other locks are gunna go too. i dunno, that´s just from my personal 2 cents worth of experience.
so it could be plain worn out, and a sign that the other locks are gunna go too. i dunno, that´s just from my personal 2 cents worth of experience.