No NPP_Stream callback

Ok, I will try it another time (some folks may remember me barking up
the wrong tree with similar issues already twice):

On Windows, with Firefox 10.0.2 I have a plugin that does:

(1) -> NPN_GetURLNotify(m_inst, url, NULL, (void*)token)

and usually Firefox responds with:

(2) <- NPP_StreamAsFile()
(3) <- NPP_DestroyStream()

Now sometimes I don't get the NPP_StreamAsFile() callback, but straight
away a NPP_DestroyStream() - with reason == NPRES_DONE.

However, since I did not receive any data in between my plugin is a bit
confused. I am realy sure the notifyData passed to NPN_GetURLNotify() is
!= NULL. And sometimes it actually works, but I have no clue yet, when
and why.

Any hints?

Martin