Olympus AF-10, frame overlap

Hello all,

Picked up an Olympus AF-10 for 3 quid in a charity shop. In fairly good condition all around, a bit of dust on the inside to clean out, but nothing too terrible. Put a new battery into it. However, the roll I put through it came out with every frame overlapping. And quite a bit of excess film leftover at the end of the roll. It seems it's only advancing half a frame. Is there a common cause for this problem?

Thanks for your help!

Egg on my face. I've just realized I put an exposed roll through it. No overlapping! Carry on.