asterisk users - Apr 2006 - ringing indication in handset when 2 extensions answer simultaneously?

I have a bunch of grandstream gxp2000's in the office.

When I Dial() multiple extensions at once, eg
Dial(SIP/2000&SIP/2001&SIP/2002) and two extensions answer
simultaneously,
one of them gets the call and the other hears a ringing indication in the
handset.

Anyone else seen this bug?

-Dan