Gzipping proxied content after using subs_filter fails

[abstein2]

I have e-mailed Yao Weibin, but wanted to give an update here regarding
my findings. It appears the issue is linked to long strings of text
unbroken by a new line. With my settings, it appears that if a line
contains ~40k bytes without being broken by a new line, something occurs
whether gzip is on or off, that causes the gibberish to appear on the
page.

Thank you all for your input so far.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,229545,229651#msg-229651