Do you have the problem only with one DECT-extension-number ??
I had a problem in one exchange with "double subscription"
-> Customer changed Portable, but did not delete the system in the old portable.
-> The old portable was in a charger, and tried to subscribe to system.
-> When the new portable maked a call, and the old PP tried to subscribe, the call was disconnected.
This can be easily seen in the mobility log, when one PP every ca. 5 min tries to locate but fails. ( LRU )
best regards,
Norbert