[TempFixed]: SCCP second line teminated on incoming calls

Hi Team,
I am operating my asterisk server since more than 3 years now, and never have come to this issue.
On my Cisco 7940 I have configured two lines.
The first one is the normal private number and the second my home office business number.
Under normal circumstances I pick up incoming calls using the headset button, which work like a charm.
Today I was receiving a call on my 2nd line and picked up using the normal receiver.
The call on the 2nd line was immediately terminated and an outgoing call was opened on the 1st line.
I tried to reproduce the error several times, and any attempt ended with the same behaviour.
An incoming call on the 1st line is picked up normaly w/o any error.

Any suggestions?

Asterisk “sccp show version”:
Skinny Client Control Protocol (SCCP). Release: 4.2.0 RC2 - 6019M (built by ‘root’ on ‘2016-09-04 08:24:25 UTC’)
Asterisk “core show version”:
Asterisk 11.13.1 built by root @ derdapp003 on a armv7l running Linux on 2016-09-04 07:34:53 UTC

After hard resetting (powercut + “#” +“123456789*0#”) the Phone and restarting the asterisk server, it seems to have gone away.