Used to see this problem a lot on PRIs, but with SLT station dialing. The fix was to deny Dial-On-Conversation (Stations>SLT>Dial-On_Conversation). I haven't fooled with an IPNet trunk in over 10 years, but do seem to recall they acted as an analog-type of connection. Try setting ALL of your SLT ports to Deny for that setting. It's counter-intuitive, I know, but try it and see.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.