Support of Tag 0x00 for Tunnel-Server-Endpoint

[Naoufel]

Hi,

I'm using free radius 2.1.9 as a client to connect to a distant server (not freeradius). 
We are facing a problem for Tunnel-Server-Endpoint attribute :

RFC http://www.ietf.org/rfc/rfc2868.txt indicates for Tunnel-Server-Endpoint :

   Tag
      The Tag field is one octet in length and is intended to provide a
      means of grouping attributes in the same packet which refer to the
      same tunnel.  If the value of the Tag field is greater than 0x00
      and less than or equal to 0x1F, it SHOULD be interpreted as
      indicating which tunnel (of several alternatives) this attribute
      pertains.  If the Tag field is greater than 0x1F, it SHOULD be
      interpreted as the first byte of the following String field.

So, there is no explicit prohibition of use of 0x00 as a Tag value.

What we see in freeradius is that this values makes as ignore the value of the atrtribute.

Is there some other RFCs that show explicitely that the 0x00 tag should lead to this behavior ?
Is it a freeradius bug ?
Any help about where is it managed in the code ?

Thanks for help