Is the virtual server under heavy load or are you just testing with single requests?
The message from CLIENT_ACCEPTED might be getting throttled if there are a lot of repeated logs with the same message ID. Do you see messages like this in /var/log/ltm?
mcpd[2239]: 01070727:6: Per-invocation log rate exceeded; throttling.
mcpd[2239]: 01070638:6: Resuming log processing at this invocation; held 22 messages.
sol10524: Error Message: Per-invocation log rate exceeded
http://support.f5.com/kb/en-us/solutions/public/10000/500/sol10524.html
Aaron