I’ve been using Misandra for quite a while (a couple years) and never (or almost never) she does additional hits on her first skill or while no enemy has fallen yet.
Skill description doesn’t specify anything about how many enemies there are, or how many times she has activated her skill. That’s why I see this as a bug:
Oh, and of course I have seen additional hits, but when the battle has passed a few turns or some enemies have fallen. It’s actually more common to see the additional hits when there’s only one enemy left.
I haven’t registered any examples but I could do it from now on. The thing is I preferred to ask first if this is intended or not. Either there’s something missing on the description, or something on her skill has an error.