asterisk users - Sep 2007 - Ghost calls from phones

Hi all,

I have since days now a strange problem with two Thomson ST2030 phones (FMW 
3.56) on Asterisk 1.4.11. They are both in a queue (only one phone per queue 
to get the MoH played ...)

No i see often times in the CDR these:

33012
	2007-09-20 14:16:52+02	 	 	s	outgoing-staff	SIP/test1-082ca1c8	 	 	 	
6
	
0
	NO ANSWER	
3
	 	1190290612.216	 


So calls to dst "s" and always different SIP channels. During that
calls I Get
back on the CLI a 
 -- Got SIP response 486 "Busy" back from 172.10.4.170
    -- SIP/reservation-b5c322c8 is busy

so the phone seems to stuck in calls and is not reachable anymore....

Any idea?

Kind Regards,

Erik