I have eight Panny plasmas and all work the way you want them to. Have you hit the "Viera Link" button on the remote? That should get you to a page where you can select "player" and they should link up.
I am familair with Viera Link and the tc-p42x5 does not offer Viera Link. It does offer HDMI control as described below from the user manual:
CEC function [On/Off] On: The TV is turned on automatically and switches to the appropriate HDMI input whenever an HDMI connected equipment is initially turned on and the Play mode is selected.
Power Off Link [Yes/No] Yes: When the TV is turned off, all HDMI connected equipment is also automatically turned off.
• A Panasonic DVD Recorder will not turn off if it is still in Rec mode.
• The TV remains on even if the HDMI connected equipment is turned off.
Neither CEC nor Power Off Link have any affect on the problem :-( Nor does the HR20-700 seem to support these functions. :-(
From my research, it seems that the remote code for toggling the tv on/off (press remote pwr button with the slider set for tv and the tv will toggle on; press again and the tv will toggle off), and the remote codes for the separate on and off buttons are all different. Perhaps Panasonic did not support the separate on and off button remote codes (but I cannot verify).
Anyway, I am hoping that there might be a solution so I am tapping into dbstalk.com hoping someone can supply one.