yeah....whenever i lost one it was usually after a feeding too and they'd just leave the still gasping for air head. i only lost 2 out of 8 that way though and it was always the largest fish they got taken out. after they ate a tankmate they wouldn't eat for 3-4 days even though i had been feeding them twice a day before the cannibalism.
were they wild RBP by any chance? what temperature was the tank generally at? did the plants/driftwood break up the sight lines? what were they being feed?
For some reason, Im lucky to not have fallen to the problem of cannabalism.. I guess the plants/dw really do "break up the sight lines" therefore the chasing is only temporary. They just seem to fight for territory. When I upgrade, I wont waste money of plants anymore. I will just use the ones I have and get one large set of fp.