Snom 320 unknown parameter

I recently received a batch of 10 Snoms 320.
I upgraded the frimware to linux V3.38, application V6.5.10 and jffs2 V3.36 just like the older Snom320 which I already have for a few months.

Problem:
I have a problem with uncondtionally call forwarding with the new Snoms 320 when pressing *21 (for the Netherlands).
With the “old” Snom320 it is no problem, even with the Cisco 7960G.

All the settings on all the webpages of both phones were equally set.
I did a comparison of the settings of de "old"and new Snom320 (1465 parameters) and saw that one parameter differs (the other differences are ip-address etc. ) which I couldn’t figure out what it function is.
In the “old” Snom it is set to Active and in the new Snom it is unset.
The parameter is “t0_1” !

Questions:

1.Does anybody know what this parameter means ?
2.Can it be set via a webpage ?
3.Is it an undocumented feature ?

ThanX in advance !