Unless the seal is fitted with a vent tube taken above the waterline or the same connection is used to feed water to the seal the seal needs to be 'burped' of air after a period ashore. Most new sailboat installations will have the vent tube (ours does) as I believe this is the only one being stocked as standard now. It is only high speed installations that need the waterfeed.
Ours has never stuck nor would I expect it too. Is the boat you looked at on a drying mooring perhaps?
-------------------- Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!