How cold does the bike get when stored? If water gets inside the ratchet (be it a freewheel or cassette) and then freezes it can cause either full lock up or spinning both rotational directions, as the pawls can freeze in their position.
When I had my shop in Cleveland the whole bike messenger thing was getting going strong. My shop was the closest to downtown (where most of the deliveries were being made) and close to where some of the messengers lived. So they would sometimes stop by on their way home. They would ask about why their bike didn't freewheel or not catch forwards when earlier in the day it ran fine. My shop had a classic hot water radiator right by the front door and I would motion the riders to park their bike by the door (as the bikes would be crusty with salty slush and would drip down when warm). They would come to the counter and describe their problem and I would say I can fix the bike without touching it if given a few minutes. Sure enough they would find their coasting/catching worked fine in a few minutes, as the puddle under the cog set grew
Flushing our the internals and adding as thick a lube as we could would offset the freezing issue for a while. Andy