Mitel to Asterisk DTMF problem

And what a peculiar problem this is:
Mitel ICP 3300 has a E1 Pri incoming and a SIP trunk to Asterisk 13, when dialing the Mitel via the E1 and only from certain sites including a Mitel site, when processing dtmf digits across the sip link we receive all digits (1-9) except the digit 0. This comes as inband as if the Mitel ignores transcoding the digit 0 but all others are done correctly.
I did a wireshark trace and found exactly that, RFC2833 only picks up digits 1-9 and 0 is inband audibly noticeable in the speech path.

I am baffled, anybody else had a problem like this?