I've got the answer from the Trolltech support.

I negliged the windows calling convention (cf article at http://www.unixwiz.net/techtips/win32-callconv.html) with the consequence of corrupts memory all over the place.

Finally I had to change my typedef from:

Qt Code: 
  1. typedef short int (*GetInfo)(unsigned char,unsigned char,unsigned char *,unsigned char *,unsigned char *,unsigned char *);
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into:

Qt Code: 
  1. typedef short int (__stdcall *GetInfo)(unsigned char,unsigned char,unsigned char *,unsigned char *,unsigned char *,unsigned char *);
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That solved everything.