Hi,
I do agree with Mats, that it is not so unusual. I would prefer, however, not to talk about "promiscuous", since at the end of the day, it´s a very human term and we are talking about animals that do not care about human moral values..
In that sence, I would a gravid female even
expect to spawn with a male guarding eggs/fry, because it has already proven being able to guard (or even raise) fry/eggs. That also fits to observations I made with different Hypancistrus and Ancistrus species (I´m only certain about those two genera because of the frequency of spawnings; others do not allow such statistical evaluation): it is usually the very same male that spawns with all females in the tank, even to the point where it starts to starve (usually, it is then replaced by another male, because it cannot be the dominant male anymore). I very seldomly have two males guarding eggs, while in some instances, there are two generations of fry plus a fresh clutch of eggs in the cave.
On the steeling eggs issue: I tend to leave the eggs with the male, no matter if it occasionally eats them or not. The only exception to that are notorious egg-eaters, that simply don´t go over the first one or two nights without eating the eggs (after countless tries), from those males, I take the eggs. The other thing is (very) rare fish, there, I tend to save the first one or two clutches, in order to have some fish to give to other hobbyists, as a contribution to preservation in the hobby. In general, I prefer to watch the male guard and raise the fry just for the sake of natural behavior.
Cheers, Sandor
"What gets us into trouble is not what we don´t know.
It´s what we know for sure that just ain´t so."
--Mark Twain