avifile doesn't close files properly

Hello,

i am using avifile in my own software project. Avifile is the greatest DivX
library, capturing and playback works fine. 
But i have the following problem:

When recording i use

  videoStream->Stop();
  audioStream->Stop();

to stop the recording. But the resulting avi file is not closed properly, i.e.
when trying to playback, i have to rebuild the index. 

What do i do wrong? Is there anything i have missed?

I have been busy with this problem now for weeks, desperately.
So i would be very very happy if anyone can help me.

With best regards,
Christian