HELP! problem with dullcote!

with the humidity, would having my reverse cycle heater on while im painting have something to do with it?

Dullcote is noted for turning white when applied during periods of high humidity - and it doesn't have to be raining to get that (the other day it was 92 here, not a cloud in the sky and we had 90% humidity).  The higher the humidity, the more likely the Dullcote is going to turn white.  I've gotten into the habit of either checking the NOAA Website or the Weather Channel to see what the local humidity is.  And as noted, you can usually correct the problem by spraying on a new coat of Dullcote.