I assume this happens only while trying to create ticket by mail, right? I am experiencing the same problem on version 4.2.12. There is a clue in /var/log/procmail/procmail.log:
HTTP request failed: 500 Server closed connection without sending any data back. Your webserver logs may have more information or there may be a network problem.
procmail: Program failure (75) of “/opt/rt4/bin/rt-mailgate”
This creates apache core dump. Last time we have investigated that this lead us to find a bug in Sys::Syslog perl module. We have reported that issue (and fix) to upstream. But I am afraid there are more buggy perl modules which RT depends on. Now this behavior occured in my RT again, notifications were sent but the ticket does not exist in database. Investigating the core dump again 
Petr