Well, Opt+Shift+= will give you "±," so if the keyboard happens to be sending a signal like that (perhaps when you press Shift), that might explain it. Obviously that shouldn't be happening, but I've used the Kanex keyboard you're talking about before and wasn't too impressed, so I wouldn't be surprised if there were a defect in yours that was causing this to happen. Is it new enough to still be under warranty? (Do they have warranty?) If so, you might want to contact them.
You might also try using USB if it's currently connected via Bluetooth (or vice versa) to see if the problem happens both ways. I'm assuming other keyboards are fine?
