Attached, a patch for this bug.

It makes hiding the output buffer until there is output the default
behavior; if the user wishes to get the old behavior back, then
display-buffer-alist can be customized to remove the new default element.

If this patch is acceptable, I can add a NEWS item and install it.

As a side effect, the process object is now made available to input and
output filter functions.

-- 
http://rrt.sc3d.org