I've ha dthis happen to me in 1.02 and 1.03 and I usually linked to POPs devoloving while in factories and not dropping out... I don't use Auto-assign, so I keep a really close eye on my factories. I fgiured it was a minor bug... and relatively easy to deal with in 1.02, but in 1.03 I can't figure out why my POPs are devolving b/ my taxes are less than 50% (49%).
I have 2 theories about this:
1) POPs are devolving b/ their basic needs aren't being met.
2) POPs are devolving b/ I'm taxing to high, and the percentage shown on the taxation slider isn't corelating properly to what the actual taxation rates are.
Either way, I beleive it's craft and clerk POPs devolving and not dropping out of factories properly. I have a save game wihch I could sned to you Derek if it helps.