You did mention it...I tried it...no success.
EDIT:
Okay...this is me right now.
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What I was doing was going into the stock gallery app and saying 'set as'...but when I went to crop the picture for the lock screen, it was sending me over to QuickPic. I hadn't noticed it was doing that...just assuming it was staying in the stock gallery for cropping.
I cleared the defaults and then tried it and when I actually selected cropping via the stock gallery it worked!
Now I feel stupid for not noticing that subtle switch.