I just ran into a scenario where I assigned a VLAN to some Aastra phones (tried both 126.96.36.1991 & 188.8.131.524) via /tftpboot/aastra.cfg as follows:
# ADDED BY ATCOM
tagging enabled: 1
VLAN id: 100
vlan id port 1: 1
However, the info didn't seem to "take". I checked it manually via the web interface and the VLAN ENABLED box was greyed out & not checked - I couldn't change it. The VLAN info was in the server.cfg file.
I assume this is a bug in the current version of firmware as I have used this setup many times in the past.