You probably already know this or when you hear it, it'll make perfect sense, but do NOT use heat on a wood stock. Ask me how I know.
The first one I did, was in the winter time and I wanted to speed up the clear. BAD mistake was putting a quartz lamp on it. Moisture came out of the stock and gave it a severe case of chicken pox....but the clear locked up really fast!
That was no fun to fix, either.
Yep, as you discovered, wood does indeed have air trapped within the fibers and the trick is to spray the finish when the temperature is falling, not rising, otherwise the air will expand out of the wood and leave what looks like solvent pops, small voids in the finish that just will not fill in with additional coats.
The trick I have used is to heat the stock or place it in a warmer area of the shop for several hours then spray the coats as it cools.
