[Osip] INFO message causes an 481 reply

[Dagani Itay-BID123]

Hello,
 
I have two user agents (A & B) which register to the same proxy.
 
After registering both, I cause an INFO message to be sent from A to B.
 
  INFO
A ----> B
 
Even before the code reaches the receiving message handler (on B), I can
see 
 
   481
B ----> A
 

B sends "SIP/2.0 481 Call Leg/Transaction Does Not Exist" to A
 
Is this because this INFO message is outside of a call ? 
how can I prevent this ? (and if I prevent this, do I break
compatibility with the sip rfc 3261 ?)
 
Thanks :-)
 
Itay