Reply/forward inline freezing until requesttimedout error

[twisterbr]

Roundcube version: 0.9.1
Web Server: nginx 1.1 with varnish 3.0 and php-apc

When I try to forward or reply a message that has some Re:Fwd: in it ('reply of the forward of the reply' kind of thing), roundcube keeps loading for ~3min and then drops the error "Request timed out". But this doesn't happen when I send the message as an attachment.

The weird thing is that the full message is received by the recipients normally.

I tried moving the message file to another user account to see if the preferences were influencing, but I got the same error.