Our home uses an updraft furnace, with return duct in the crawlspace and supply in the attic. I noticed yesterday that there was cold air blowing OUT of the returns in 2 bedrooms that are farthest from the furnace.

I'm assuming this in not normal... any ideas as to a cause?

The cold air comes before the hot air when your furnace comes on and if you live in a very cold climate as I do (southeastern Lake Ontario), that happens.
The cold air is is being driven out by the hot air and it stands to reason there will be more of that in the duct work farthest from the furnace.

However, I may be wrong, but it sounds sensible to me, as far as I have noticed.

Tick

You're misunderstanding... I am not talking about cold air blowing out of the supply in advance of the hot air, I mean that cool air is being blown out of the RETURN duct while the furnace is in operation.

Could this be a pressure issue?

The return ducts are connected to the supply somehow OR it is so cold the heat in the duct is being lost by the time it gets to the remote location.