It's a known bug for sure with fishing, cooking and first aid. Blizzard knows about it, and has known for a LONG time. You are pretty much SOL til they do something. sorry...
And you aren't the only person with the bug. many people have it. I was lucky enough to not be bugged.
Basically with all of them when you finish the quest to reach 255+, you simply are NOT allowed to advance in skill. It's that simple. For anyone who hasn't heard about it, I suggest you browse the Profession forum on the official WoW forums, many people have posted there, and there are some FAQ posts that help describe it better.