Airlock backing up?

I've been brewing beer since last December and have always used three piece airlocks. This spring I tried a dandelion wine when all the dandelions were plentiful. I'm using the same type three piece airlocks for the wine. I started in a bucket on 4/29/'12. I racked to a carboy on 5/7, then again on 7/28, 10/7, and 11/26. Yesterday I looked at the carboy and the water in the airlock was most of the way up the center tube. The top floating piece was down on top of the tube, not up like it has always been with my beers. I tried to remove the airlock and some of the fluid from it went over the tube into the wine. I'm not too worried about contamination because I use vodka and distilled water in my airlocks, but I still don't like it. What causes this and how do I prevent it? The room is staying the same temperature. Should I use an S shaped airlock for wine? Thanks for any advice.

Only thing I can think of was temp change. A cooling of the liquid would cause it to contract, causing negative pressure. Was the batch warmer when you racked it on 11/26 and its gotten cooler since then?

Common effect of swift barometric pressure changes. Have had it occur with either type of airlock.

To WilliamSlayer, no, the temp has been the same, right about 70. saramc, I guess it could be a pressure change, but if so it didn't affect any of my fermenters with beer in them. Yesterday I switched the airlock to an s type and it seems to be bubbling backwards slowly.

Lol, uh oh... Reverse Fermentation!?! The end of the world really IS nigh! ;-)

Well, maybe SOME people believe the Mayans, but I don't. Today the fluid in the s lock is going the normal direction. I think I'll use an s type for all my secondaries from now on.

Yup, reverse fermentation. Usually this only happens in Australia where they must use a centrifuge to remove yeast from wort to produce alcohol.

One thing you can do is fill the airlock with less liquid. There's a range where it will bubble in either direction.

Right, if I keep the s airlock fluid at or below the fill line, it works either way without sucking into the fermenter. With the three piece airlock, it sucks in regardless of the level (other than empty) if it goes the wrong direction.