Call forward problem


We used the newest FreePBX Distro with Grandstream GXP-2000.
Everything works great, except for one thing.

An incoming call is displayed correctly (e.g. 0721XXXXXXXX).
But is the phone forwarded to another phone the incoming number displayed incorrectly (for this example: 00721XXXXXXXX).

Call forwarding is set up with the key combination *740. (Same result to external mobile phone and internal ring group)

Is there a possibility to remove the second leading zero?

Many thanks in advance.

Greets Stefan