asterisk users - May 2006 - Wacky Failover Situation w/SIP - Bug?

I have a weird situation. A polycom phone is configured to use system pbx1 as
the primary outgoing 'proxy', followed by systems pbx3 and pbx2. All
three systems have identical sip.conf files. The phone is registered on pbx1.

I shut down the Asterisk application on pbx1. I make a call. The phone sends an
INVITE to pbx2. Pbx2 sends back a 407 Proxy Auth message to the phone. The phone
sends an ACK followed by the INVITE with the credentials. What does Asterisk do?
It sends the 407 Proxy Auth message again. Why? The phone of course re-sends the
INVITE with the credentials again, and of course Asterisk sends the 407 again.

After some period of time, say around 5min, it all starts working again. The
phone still has not registered with pbx2 yet. The phone sends INVITE, Asterisk
sends 407 Proxy Auth Required, the phone sends an ACK and an INVITE with the
credentials and Asterisk sends TRYING.

It looks like an Asterisk problem. As far as I can see, the phone is doing the
right thing. Asterisk should not be sending Proxy Auth required over and over
again.

Also, if I change the sip password for the phone while this is happening to
something bogus (and do a 'sip reload'), Asterisk still sends the proxy
auth over and over. It obviously isn't reading sip.conf. This looks like a
bug to me, but I can't work out why Asterisk is having a problem routing a
call?

Doug.