caliper problem

hi guys n girls. Having some trouble with my front right caliper....
I changed the seals a while ago due to corrosion and a sticky piston! after this all seamed fine! but after having my tyres changed yesterday i noticed a low speed squeel coming from that caliper. i removed the caliper this morning thinking a quick clean would be all that was required, but the opposite piston is now sticking (i made sure they didnt get swapped over upon refitting). the seals are still in tip top condition, the pistons are clean with no pitting, so what gives? could air trapped between the seals do this? if so how would i get around this when re-installing the piston? there is no air in the system what so ever, and brake travel seems no different to before, no sponginess etc help im stuck