asterisk users - May 2006 - Unwanted conference with snom320 and asterisk 1.07 bristuffed

I have 13 Snom 320 with asterisk 1.07 bristuffed. The problem is that
sometimes on random basis, when one customer is placed on hold and another
call arrives, the customers are put in conference with each other. This look
very strange to me, but I've disabled the confernce button on the snom
phones to prevent the human errors, but it still occurs. 

Investigating I've discovered that a similar problem was fixed with the
Snom320 Release 5.2  (http://www.snom.com/snom320_release_notes.html ) 

It says: 
fixed unwanted conference bug in offhook/enter during ringback with an
incoming call 

BUT my phones are already running 5.2 firmware. 

Any idea? 

Am I the only one with this problem? 
Do you think is the usual  buggy-snom firmware problem? Or it might be an
Asterisk problem? 

 
 
 
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