If you find a bug or think you find a bug, it is very important to report it.
Ther is a bug (i think) in transfer *2 and #1 the option both dont work
This Issue was resolved in version 3.1.1, see the changelog at:
Not by me, i use 3.1.1 but the option both dont work. SETTINGS DIAL-PROFILE GENERAL DEFAULT
and select BOTH only ONE site can transfer.
I try it futher with more different IP stations maybe there is a problem with the YEALINK software or the GIGASET rom.
Greetings Rob van den Bulk