Cleave not triggering upon blow with offhand weapon

[Nylo]

Wielding a non enchanted bastard sword in main hand, and +2 nunchaku in off hand, I'm noticing that striking the killing blow with my offhand weapon does not trigger cleave, while my main hand will trigger it normally. Power attack was off, and my dual wield is at amateur. I don't know if it rolls against dual wield skill, if it does it is likely not a bug after all.

EDIT: With dual wield at JM, I've seen many killing blows struck by my offhand weapon, and none triggered a cleave. It doesn't appear that it's rolling against dual wield.

[Vibius]

Tested and confirmed in the testport. Perhaps affects any other skills that trigger upon hit (sneak attack the only one I can think)