Has anyone experienced this issue of disconnect. I have a ticket open, but no success fixing the problem.

Starting about a week ago, I receive a disconnect when answering a random incoming call. Doesn't always happen, but today I received an incoming call on port 1. When I answered the line was dead, really dead as in no talk voltage from the ATA. The zero voltage was also shown on the port 2 line. This lasted for about 5 seconds after the phone on port 1 was returned onhook, then everything returned to normal dialtone on both ports. The incoming call went to VM. I am using the VoIPo HT502 connected directly to the cable modem. Internet access was not affected. Even when not registered, the ATA provides sidetone voltage and a device not registered message. Did not receive any message and see zero port voltage. Could be a defective ATA?