Shimano Sora shifter having trouble in the snow So today is the first day of snow here in Norway, and I had prepared well for this day. My Giant Cyclocross has new spiked tires and i've done a check on all components, they are ready for the winter-commuting.

When I got to my first climb on my way to work today, I noticed my right shifter wasn't working. I got Shimano Sora shifters, and Tiagra derailleurs. I could flip the shifter, but the gear wouldn't stick. If I held the shifter flipped, the gear would lower, but as I released it, it would jump right back. This happened after just 5 minutes outside in the heavy snowfall. It was as if the mechanical inside the shifter wasn't working. 
I store my bike indoors at home, so my bike wasn't frozen when I got on, and I don't think its below 0Celcius outside even. 

My bike is only a year old, and I haven't had any big troubles with either shifters or derailleurs before. This is my first year riding it in the snow.

Is this a common problem with the cheap shifters? Is there anything I can do to help/prevent sticky shifting? 

edit: It seemed I could shift into a heavier gear without problem (loosening cable tention), but shifting into a lighter gear( thightening cable) was close to impossible. 

Edit 2: After the whole day inside my shifter still won't work. I'll open the shifter up this weekend and see if I can find the problem.
I opened my shifter a bit, not disassembled the whole thing, but I was able to degrease it well. I then applied a lot of spray lube. I shifted up and down while spraying, making sure the lube got everywhere. I have used my bike every day in cold weather now, one day as cold as -10Celcius, everything seems to work. It can be a bit sticky, but I always manage to shift correctly now. I guess I'll have to apply lube quite often now, the spray isn't as heavy-duty as the original grease, but my gears work now.

Edit: I took my bike to the shop today, the shifter has gotten worse the last few weeks. When I picked it up they said Shimano has called back several models, a faulty spring seemed to be the problem. I got it replaced no-cost. My new shifter works perfectly in the -5C now!