Vendor-type length problem

[MINODIER David RD-RESA-LAN]

HI all,
I have a Radius client (not generic but proprietary) that encodes its
vendor-type on *2* octets while the "normal and common" way is to encode
the vendor-type on 1 octet (0-255).
RFC 2865 says that the actual "vendor-type + length + value" is a string
field and :
"The String field is one or more octets. The actual format of the
information is site or application specific, and a robust implementation
SHOULD support the field as undistinguished octets. The codification of
the range of allowed usage of this field is outside the scope of this
specification."

O'Reilley Radius book however says page 28:
"vendor type - the vendor type field, which is one octet in length,
etc".


And the consequent questions: 
- Is there an RFC that actually defines for good the length of the
vendor-type? (I did not manage to find that piece of information)
- can Freeradius encode a vendor-type on 2 octets for 1 specific vendor
while replying to the client? 
- if so (I doubt...), how? (configuration? Special dictionary format?)

Many thks.
David.