The Cardassians and Romulans possess an item which prevents changelings from altering their shape, a device which would have been extremely useful for the rest of the series. It is never mentioned again.
When the Defiant is leaving Deep Space Nine, Sisko orders "aft thrusters back one-quarter, port and starboard thrusters at station keeping." The aft thrusters push the ship forward. He should have ordered "forward thrusters back one-quarter..." since the thrusters at the front of the ship push it backwards.