If you connect a comparator's output to one of its B inputs, put it in subtraction mode and power the A input, the output signal starts to pulse rapidly.

This is not a bug, but if you connect this pulsating signal through a repeater into a dispenser, setting different delay times on the repeater causes inconsistent behaviour at the repeater and the connected dispenser.

I talk about this in the following video:
http://www.youtube.com/watch?feature=player_detailpage&v=7uV1ZLI7Tg8#t=68s

or, if the upload works, i attached the relevant part of that video to this report