Warped rotor or a rotor with quite a bit of runout in combination with a really sticky caliper piston? Just a thought. Anyways since the problem surfaced at the last thing you did it is more than likely involved. I would want to make sure the caliper pistons will slide into their cylinders without much resistance. Again a one side to the other side comparison is a good yardstick.
You moved the pistons to a new operating area when you installed the new pads remember. The rust on the new area of the piston now being used if present could bind on the seals. Just something I would check out and does not mean it might not be something else. Double check that the wheel bearng is not loose but since you did not have the rotor off it is probably okay. You can jack up each side and check or compare one side with the other. Check tire turning resistance and check for same amount of play in and out etc.