Font or Paint Engine

hello
I encountered a problem when running the program in wince,I remove the sd card,then insert the sd card,when i restart the program the chinese which is drawn in QPushButton or QLabel will be drawn garbled.
so I to debug in qt's source code,i found that when the QPainter call drawTextItem,in QRasterPaintEngine,it always draw catche,and the QFontEngine::Freetype's code will never be run.why??? if i don't want to draw cache how can i do?
The team leader told me that i need to use freetype to replace qt's font engine.But in qt's source code has alreay have this but it does not work.In your document,you told us that "If one wants to use QPainter to draw to a different backend, one must subclass QPaintEngine and reimplement all its virtual functions",I don't known how to set my engine to the painter,or can you give a example if possible.I have try a another way,i use paintEngine()->getDC(),then i can use the HDC in freetype to draw,i don't think this is a good way.but now I have no way.Do you think is this your problem??
Thank you!