Yes, slipping freewheel / cassette is very unnerving. You need thinner lubricant for the pawls (the procedure is described in the Icebike web site). I suggest you do this if you ride frequently in cold temps, as you certainly do not want it to slip when you're cranking up a hill, for example.

I just saw a guy outside a local auto parts store, feverishly spraying his 8 speed cogs with a lubricant. The cogs were turning freely every which way, he knew what the problem was and he also realised he was not going to fix it with spray. I think he finally took his bike inside the store to defreeze. And it was not even that cold, maybe -7C or something. I hope he came out all right.

--J