T38 Passthrough - T38FaxMaxDatagram default value?

I have a Asterisk (ver with T38 passthrough in the following setup -

SIP Trunk Service Provider – Asterisk – Quintum GW - Fax Machine

When sending Fax, the 200 OK response from Quintum does not contains T38Faxdatagram Attribute; and from the following debug messages

[Nov 26 10:54:14] ERROR[8980] udptl.c: Buffer overflow detected (6 + 3 > 0)

It seems that Asterisk treat T38FaxMaxDatagram (no attribute in response) as 0.

Since the T38FaxMaxDatagrami is an optional parameter in T38 spec; how to interpret the “none exist” parameter in 200 OK response ? can we assume it is 0 (as implemented in Asterisk) or we should consider it as the confirmation of using our T38FaxMaxDatagram value in Re-Invite.

Thanks for any comments.