VVX410 Making automatically calls on its Own

I have VVX 410 in my organization.

We are starting to notice that over the weekend these phones are making calls on their own. My managers phone for instance, in an office with the door closed over the weekend, his phone placed a call on its own, on a sunday afternoon

our lync activity reports confirm that it is his phone placing the calls because it keeps track of mac addresses that placed a call

i've seen a similar issue where this had happened:

http://community.polycom.com/t5/VoIP/Phone-calling-random-contact-on-display-amp-Auto-Answering-on/td-p/41407

however the phones that we have deployed don't have touchscreen's so its not necessarily the same issue.