I have three amps: two combos and a head+cab. I usually use two amps at the same time and I had to make sure all the speakers are in phase so I had to switch the wires on the speaker in one of the amps and they're working fine. Even when I'm running the three at the same time they're all in phase with each other. Yesterday I had to run the head through one of the combo's speaker and I noticed that, when paired with the other combo, they're out of phase! When I'm running both combos together they're in phase but, the head seems like it's flipping the phase! Is that possible?