asterisk users - Dec 2003 - Strange * & ATA behaviour when directly connected

Hi,

This is my  very strange problem:

I have connected * server and ATA186 directly through a cross ethernet cable
(isolated from the rest of the network).
I have two extensions (101 and 103) connected to the ATA.
When an incoming call on X100, both phones must ring.
This is what I have in the inbound context:

exten => s,1,Dial(SIP/101&SIP/103,60,tTr)
...
When an incoming call arrives, just extension 101 rings and for the other
one I get the following in the * console:
SIP/103-e532 is circuit-busy

I can place internal calls without any problems in both directions
(101-103).

If I change the line in extensions.conf like that:
exten => s,1,Dial(SIP/103&SIP/101,60,tTr)
...
extension 103 rings, but 101 now gives:
SIP/101-e513 is circuit-busy

Why changing the order in the dial string gives me this issue?

Connecting the * and ATA in the local network, this problem disappear.

Anyone knows the cause?

Thanks,
Dan