Note, I'm pretty clueless about mod_perl. But looking at the changelog for mod_perl 1.xxx, there are a few items that look like they might be relevant somehow, like:

    fix $r->read() so it will not block if all data 
    has already been read and so that Apache will not 
    hang during ap_discard_request_body() on error or 
    redirect after all data has been read
[download]

Is there any way you could try it under the current version (1.27)?

In any case, browse that changelog, I'm sure those items will mean more to you than they mean to me.
--
Mike