I came across this posting and he appears to have some similar
experience.

http://groups.google.com/group/rec.w...cce9aecda368a1

'The plywood dart-board cabinet puzzles me. I painted the back with
exterior latex. Then, I applied a few coats of clear Minwax
Polycrylic (water-based *interior* finish). The Minwax label said not
to do this. Don't ask me why I did it -- just a crazy afternoon
playing with the chemistry set, I reckon. Anyway, after six years of
brutal Florida sun, rain, storms, hurricanes, humidity, etc., etc. --
that Polycrylic film looks brand new! I have no idea why; I had no
right to expect that kind of performance. But there it is. Go
figger. '