It's a bug in Pango::Context::get_font_map(). It should get its own reference to the font map, but it doesn't. Until the bug has been fixed in pangomm, you can add a reference yourself.
auto fontMap = context->get_font_map();
fontMap->reference(); // Temporary bug fix
Note that when you start using a fixed version of
pangomm, the call to fontMap->reference() will cause a memory
leak.
does the error occur if you do windows.reserve(2) before the emplace_back()s?Yes _______________________________________________