[Serusers] sl_send_reply: I won't send a reply for ACK!!

[sip]

I've gone through my ser.cfg and actually REMOVED every single sl_send_reply
in an attempt to figure out where I've got these stray ACK messages being sent
a reply, but even with NO sl_send_reply commands in there, I get that cursed
message in the logs -- usually when dealing with reinvites (which I appear to
also be having some issues with atm). 

Is there something ELSE... some module or some such that might be causing this
error other than a straight sl_send_reply command? 

N.