I'm pretty sure you have an issue with HDMI Control. Once you power up the devices sense the other is there and light up.
From the Denon web manual : (
Denon AVR-X2700H Web Manual )
HDMI Control
If you connect the unit and an HDMI Control function compatible TV or player with an HDMI cable and then enable the HDMI Control function setting on each device, the devices will be able to control each other.
Power off link
This unit power off can be linked to the TV power off step.
Audio output destination switching
From the TV, you can switch whether to output audio from the TV or the AV amplifier.
Volume adjustment
You can adjust this unit’s volume in the TV volume adjustment operation.
Input source switching
You can switch this unit input sources through linkage to TV input switching.
When playing the player, this unit input source switches to the source for that player.
I think Panasonic calls it Vierra Link. Just disable it and the auto starting should go away. See page 25 of the manual (
Panasonic DP-UB820-K Manual )
I hope this is helpful.