Bad amp? Channel out of phase? Lol what?

[david in germany]

Ok this has me baffled, I installed my little Arc Audio KS125 to run my subs temporarily in my BMW. They are Earthquake SWS 8's in the stock location. Anyways when I first hooked it up I had 0 bass because one sub was out of phase (so I thought) I had the amp receiving signal from a loc off of the rear speakers (could have had one of the rears reversed as well but no matter, I had bass again. Fast forward to yesterday, I finally had the chance to run my RCAs from the deck to the amp and pulled the LOC out, figured sweet, get the phase thing sorted as well... No dice! The one channel was still out of phase, I swapped the speaker wires and bass happened. So I disconnect the positive and try to set the amp with my DD1.... No signal on that channel.. WTF? I stick the DD1 on the negative of that channel and it detects signal.. WTF again! There is no phase switCh on this thing and the only explanation is a amp wired internally wrong... Anyone else ever seen something like this?