It seems to happen that way sometimes.
You need to clean the pins, & the cavity in the mounting bracket real well with brake parts cleaner, then grease em' up real good with some fresh caliper grease...(after they've dried from cleaning)
Get caliper grease at your local purveyor of all things automotive.
Otherwise, not only will your calipers be more likely to hang up & drag, the pins can become seized in the hole & the head will snap off next time you try to remove them...
(don't ask how I know that...)