Client claims T26p is autoanswering

[imfloridaguy]

I've had about 10 T26P's at a client's site for about 60 days.
Today the client called and claimed that they've had about 10 instances where a phone simply answered itself and they heard the caller on the speaker phone saying "hello, hello??".

The calls come into a ring group, which rings 8 phones.
In the case of the auto answering, the calls rang without getting picked up. I'm not sure what the timeout was, but around 35 seconds I think.

Anyone have an idea of what could be causing this?