Ah ha.
An error in ferret logic.
Some time ago, to fix an AI bug where the computer was using Inspire type effects in silly situations, I caused any such effect to evaluate to 0 if the target's last action was a Basic Move.
...but I made this check happen in such a way that it actually does this even if the target is an enemy.
Normally, that'd be fine: the AI has no real interest in a 0 move and will never *choose* to do one. But, "random effect" logic, like Leadership's untargeted proc, will allow a 0 eval to go through... and it is worth noting that a 0 eval does not mean "no effect" necessarily. Indeed, this would probably often cause monsters who had just moved into range to get a free turn. mutter.
Well, it's fixed now.
Thanks again for the report!