Kubuntu 10.04: Own project won't used Oxygen

Hi all,
my self-written programs won't use the Oxygen-Style anymore after I've reinstalled Kubuntu 10.04.

I don't know why it won't work; qtconfig for example shows the Oxygen-Style.

I have traced the loading of the Libs; my program tries to open oxygen.so, but the GUI has some ugly default-style.

I tried to force the Style by using QApplication::setStyle(), but doing so I can only force the Program to use i.e. Motif, but not Oxygen.

I have compiled the program with the QTCreator from the Ubuntu package sources, and also with the QtCreator directly downloaded from Nokia (Build February I think).

Does anybody have an idea what is going wron there?

Regards Mr.Green