I asked a friend about this:

I don't have a solid answer to your question about bees flying upside down.   It may be that they, and flies, will do this, but it may be only briefly, in preparation for landing on a surface like a ceiling (underside of a flower petal?).   That said, I can also see that if snow gets them confused in flight about which way is up (normally, it is the part of their visual field where the UV is brightest), then it could lead them to crash into the snow.    If this is the case, then they are crashing into the snow not because they are trying to fly upside down, but because in trying to fly upward they are actually flying downward (which is, I think, what you are thinking is going on).  

Hope you and your bees are wintering well.
Thomas D. Seeley

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