when a port pin is set it is reflected in 2 places one in latch and other on pin.the condition in latch is totally dependent on what u write at that port.but status on pin is a combination of ur setting and external conditions like load.in ur case its short in some cases it could be a transistor b-e junction.refer datasheet.it explains it nicely.
as for clearing pin simply write 0 at it.
regards
pranav phatak