Buddy of mine and I were dueling and came across this interesting bug.
Steps:
1. The warlock need to be channeling a spell at the target (IE: Drain Life).
2. The warlock needs to spin 360 degrees whilst channeling.
3. The warlock is now free to cast any spell at the other person regardless of positioning in relation to the target. (IE: You can cast incinerate with your back to the target).
This could possibly work with other classes and possibly in battlegrounds.
Tested and recreated numerous times.
Cheers.
EDIT: I have noticed something similar on my Mage, I think it is a casting bug, as opposed to a channeling bug... but that isn't confirmed yet..
EDIT2: This was used in a cross realm area, (Gold Shire)