It is an additional feature, which has nothing to do with the existing bugs about QT4. However, for most CJK users, their fonts do not contain bolden and bolden+italic style, which is used in KDE programs and many web pages. In GTK, it is reproduced by freetype, but Qt does not contain this module. Here are the two patches which are already used in most other popular distribution and gentoo-taiwan overlay. If directly applying the patches are not suitable, maybe a USE flag setting can help. Thank you for your work and response.
Created attachment 220929 [details, diff] Patch 1 It works on qt-4.6.2, also.
Created attachment 220931 [details, diff] Patch 2 It works on qt-4.6.2 also.
Created attachment 220933 [details] Ebuild I am using.
You should submit your patches upstream... we aren't familiar with that code, so we are unable to properly review them, I'm sorry.