IAX2 switch doesn't work / works only partly


I’ve set up two servers. SrvA and SrvB.
In SrvB I have a switch satement to connect to SrvA if no local extension matches on SrvB.

This doesn’t work but analyzing the IAX2 packet transfers with ethereal I get a clear DPREP (dialplan response) from the remote SrvA reporting that my number matched (dialplan status = 0x0001).
But SrvB then exits with the message “Extension can never match”.

Asterisk Version on SrvB: SVN-branch-1.2-r17702 (built 6.4.2006)
Asterisk Version on SrvA: 1.2.4-BRIstuffed-0.3.0-PRE-1k


extenstion.conf: (in SrvB)

; entry point for every device on the internal ISDN-bus dialing…
include => local-lookup
include => SrvA-switch

; local extensions on SrvB
exten => _[*]2XX,1,Dial(mISDN/2/${EXTEN:1})

; switch to SrvA
switch => IAX2/SrvA/mycontext