User say keys are sticking, but it seems to be only in-call dialing-DTMF issues? Or is it the Polycom phone?

The time they notice it the most is when trying to enter the ID/PIN for calling into conference calls (not on the local FreePBX server). Is there some way of tweaking DTMF that might make it more reliable? The phone is a Polycom IP7000 conference phone, and I’ve found Polycom to be generally reliable hardware wise (and I can’t get it to replicate, but I believe the user is seeing the issue). Any suggestions?