That can happen if this series of events takes place:
- Lower flaps
- Lose 1 flap
- Retract flaps without realizing the problem
- Lose 2nd flap.
Now the first flap is jammed down, say 2 or 3 notches. The second flap is either jammed "up" or at 1-2 notches. You still get a drastic roll to one side.
Had that happen in a P-40E once. Lost 1 flap 2 notches, the other 1 notch. Made for a very slow and manual RTB (you can't engage autopilot like this)
EDIT: Also, if you lose 1 flap at 3 notches, but you only lower the other side 1 notch, you're going to have a major handling issue. If you lose 1 flap at full, you need to bring the other side all the way down. If the flap was working, you may simply not have "matched the other side" properly.