On my office system we are having some issues, but every time I try to go in System Administration, connect the System Monitor and go to the System Output->Message Print->History Log tab, it only show SIP signalling logs and it is filling the history file (not just errors, it looks like all SIP messages)... if I watch the live message print, there are no SIP message and there is history messages.
I would imagine someone, some time well before I worked on this, turned something on to put SIP messages in the message print logs, but never turned it of... and I can't for the life of me find where this is set.