If there *are* other allies on the field and not extremely far away, then actually, yes, they will try to avoid fighting and stall until help gets there, provided the ally is not fighting someone else already. But this only happens when smaller ships are facing larger ones, the target isn't overloaded, and the smaller ship isn't already engaged and doing well, according to some set of criteria.
This is the sort of thing where it's really hard to say whether what the AI is doing is correct or a bug, because so much depends on the context. "Not engaging an enemy ship when it theoretically might" could be the intended decision, or not.
If you can point to a simulator 1-1 (with details regarding the loadout, and preferably without officers involved, if it's still reproducible without them) where the behavior happens at least somewhat reliably, that would be a great help. Barring that, video of the incident is also helpful (though, of course a bit much to ask for in most cases). Short of these, I really can't do anything useful with this, unfortunately. It's just not clear-cut enough to point to anything specific or even be sure that it's a bug.
I did just now experiment with overloading enemy ships in the simulator, and the ship behavior seems correct - the non-overloaded ship closes in and attacks. It's not reckless about it, but it's certainly not backing off.