Did you remove BOTH brake pads on the same caliper and THEN push back the pistons? If so, what can happen is that one of the pistons gets pushed out too far allowing the seal to fold.

The correct method is to remove one pad, push the piston back into its bore and install that pad. THEN pull the other pad and push THAT piston back into its bore and install the new pad. This prevents the pressure from the pressing of one piston from pushing the other piston out too far.