Asterisk disconnects the wrong call

Asterisk Asterisk Support
1

I have the following dial setup:

exten => 1,3,Dial(SIP/2800&SIP/2801,60,r)

First call comes in and is setup correctly.
Second call comes in and is setup correctly.
Second call is disconnected and the first call is also dropped.
Not sure if it happens all the time but very frequently.
Nothing can be seen from the standard logs.
Somebody, any ideas?

I use Asterisk 1.2.24