SDL_Mixer:Mix_OpenAudio() crashes when called multiple times

Hi there.

i have a program where i want to set the size of the audio buffer dynamically.
it works. but it works only like 3-4 times.
before i reinitializing i allways call the corrseponding Mix_CloseAudio()
(immediately) before Mix_OpenAudio(…) with diffrent settings.
i can reproduce this behavior by writing a simple main program with the
following lines.

Mix_OpenAudio(…)
Mix_CloseAudio()

Mix_OpenAudio(…)
Mix_CloseAudio()

Mix_OpenAudio(…)
Mix_CloseAudio()

Mix_OpenAudio(…)
Mix_CloseAudio()

Mix_OpenAudio(…)
Mix_CloseAudio()

where the first 2-4 times work and then it crashes with i think an nullpointer
exception in the mixer dll.
im using visual studio 2003 .net under win2000.
what causes this crash?
how can i avoid it?
thanks in advance!