We installed a wood stove with flue. It has been pretty cold lately, so we have kept a fire going (not big) for almost a week. The flue is 6", the ceiling is about 13' above the floor, there is attic above - maybe 42" (scissors trusses), and the flue has a cap.

The flue inside the house is standard stove pipe - I think each piece about 24". There are now drips coming from one of the joints up near the ceiling. I have not gotten out the ladder to find out if the drips are water, but am guessing it is. There doesn't seem to be water inside the wood stove - but I would guess the fire would cause any that got that far to evaporate. There are no water stains on the ceiling (thank goodness)

Why would this happen? What should I do about it?