Motorola's Officicial Response to this problem:
Response (Motorola Technical Support) - 07/07/2009 03:52 PM
Valued Motorola Customer,
Thank you for choosing Motorola. I apologize for the inconvenience you are having with your product.
I understand that you are having problems with your DCX3400 switching from 1080i to 720p. I will be happy to provide information on why the box switches.
The box will find what display modes your TV will support and adjust its own settings accordingly. The TV and the STB has to make a HDCP handshake anytime you change input modes or turn off your TV. The only way to get around the problem of HDCP forcing your STB or (Set-Top-Box) to display at 720p is to use component cable which will still support up to a 1080p signal. Component cable does not use HDCP like HDMI does to establish an audio/video connection between your STB and your TV.
Please visit our web site at http://broadband.motorola.com/consum...rt/default.asp
to access your user guide and frequently asked questions about your product.
Motorola Technical Support