Nope, the calipers themselves are identical.
I'm betting the problem was that the brake had the wrong adapter on it. There is the Front adapter and the Rear adapter. On the box, it is marked front or rear, and on the adapter. The rear is "taller", so to speak. Larger in general. The front is smaller. Get the front adapter on the back and you'll have major problems. Get the back adapter on the front and you may not have any pad on rotor contact.
Believe me, I know these things inside out, worked on MANY sets.
Also, make sure you have the gimballed washers (the ones between the calipers and adapters) arranged properly. Only when they're setup properly will they allow the caliper to move in its range of adjustment, and line up properly with the rotor.
I realize the bike's fixed, but this is good for reference in case someone else has the same problem!
And Old_Dude, you didn't PM me back! I didn't know what your most recent questions were, so I wasn't able to help you out more!
