I have found I needed to do the following:

If there isn't enough data to flesh out the requested number of frame bytes to return, return the truncated number of bytes extended with empty (0x00) bytes to equal the frame size. This extended data is returned with paContinue. This should keep the stream from being closed prematurely.

However, my code knows when no more output is expected, so I close the stream at that point. When new output is available, I check if the stream is inactive and attempt to start it. If this fails, I stop, close, and reopen the stream.