Never played the game to be honest, but reading around a bit, I wonder if the following will help you?
http://us.battle.net/wow/en/forum/topic/1126993152
It looks this piece of advice (from the link above), helps others with a similar problem;
Completely exit World of Warcraft
Go into the World of Warcraft folder
Go into the WTF folder
Open the config.wtf file with Wordpad/Notepad
Add this to it: SET fixedfunction "1"
Save the file
Close the file and folder(s)
Log onto the game and see what the results are