We have an Adix system that connects to another via an IPNet card - not sure if I'm using the right term, 4 channels via the network, in the db shown as Digital E&M Tie. When pressing 9 or a Line key calls route via those channels to a PRI in the ECS on the school campus. If the destination has a menu requiring DTMF digits, the Adix site can't successfully send digits. The initial call always completes successfully.

If the called destination prompts to press 1 and 1 is pressed from a digital phone, the result will be "11 is not a valid extension" - same with other digits. When listening - pressing a digit will result in a solid half second or so of the tone followed by the same DTMF tone maybe a quarter of second or less in duration.
It doesn't happen with local COs in the Adix. Doesn't happen if I manually dial an IPNet trunk followed by an access code of a local analog trunk in the ECS.
It's only when the call routes normally to an IPNet trunk to the ECS and goes out over the ECS's PRI. Supposedly back in January a reset of the ECS resolved the trouble - but I'm not so sure, it's just what I was told. Like in January, I reset the Adix and scheduled the ECS to reset that evening, same results. For now I asked the customer to use an access code for a local CO in the Adix when placing a call to the business with a menu.

I even went to another school several miles away to simulate the routing. Selected an IPNet trunk, then 9 + our office, the called party heard the double digits. That school and another typically route over their local COs so they don't have the trouble. At this point we're not sure what to try next. Maybe there was some kind of network QOS change?