http://bugs.winehq.org/show_bug.cgi?id=32427
--- Comment #1 from Nikolay Sivov bunglehead@gmail.com 2012-12-20 09:17:24 CST --- My guess would be that TCanvas getter for Handle property invalidates underlying HDC when you request it, probably it selects some font in it and we start using it when callback returns. Is it possible to reproduce that with Lazarus so we could dig into VCL code?