Unicode Text display wrong in Button

I have some trouble to show Unicode text in QT Symbian. In Label and Text Edit my Unicode text display correct but in Push Button ( and Tool Button ) my font is fault.
You can see my attack image for more infomation.
In Windows XP and Linux my Unicode text display OK. It's only fault when I use it on Symbian OS.

I'm using : S60_3rd_FP2_SDK_v1.1
qt-symbian-opensource-4.6.2
Carbide.c++_v2.3
Language: Vietnamese
I have tested in Emulator and Nokia E63.