found this one by accident ;D

set to only accept gems, fed by relocator
sent a bunch at it, when relocator going into it was stuffed, opened hopper .. only 4 stacks
i can manually place a stack in last slot, but not automagically via relocator :(

edit: using it as a regular hopper with filter is fine, it just seems to be when fed by relocator

Thanks for reporting! Woops, will fix now :)