Although not an expert by any means, I have stained wood for many years and have never seen this phenomena before. I have put two coats of stain on several pieces of millwork, and then began putting two coats of poly on it. Both products used were MINWAX. Sometimes on the first coat of poly, and sometimes on the second, a cloudy finish appears in some spots. It is very random and only on small portions of the pieces. It seems as if something is leaching out of it. This is all new wood (pine and oak), no refinished pieces. Some were perfectly fine, as I have always experienced in the past. Others were not. I did nothing different in any application, and did it the same as I have in the past. I followed the directions on the can for dry times. A photo of a particularly bad piece (oak) is attached (I think - it is the first time I have posted and I am computer challenged). Any help would be appreciated.