Recently I have DTMF issue with NEC SV9500. I did have ticket with Dialogic and Dialogic support replied.
The first comment from looking the below is that the ReINVITE is sent directly after the ACK received and causing an issue as well for processing in that case. Please see following technote where application needs change to handle the 491 pending situation.
PowerMedia HMP rejects a re-INVITE with 491 Request Pending (dialogic.com)
This call the DTMF couldn’t send from 10.92.8.13 to 10.92.38.27.
DTMF.zip
