Had a similar problem with an LG TV.
Seemed to be a conflict between the TV being set to auto scan for the best quality set-up for the PS3, i.e. 1080p, yet my PS3 was set to not allow an auto scan and insist on a 720p picture. Don't know why.
It got sorted by pressing the on button on the PS3 and keeping the button pressed until you hear two beeps, this resets the video settings. Worked for me.
If this doesn't work you may have a faulty Panasonic.
http://www.avforums.com/forums/lcd-led- ... g-ps3.html