Then you are probably losing HDMI sync. between the two. Try the following steps, if that doesn't work you may need to factory reset the TV or alternatively phone Samsung and ask them to guide you through resetting the HDMI ports via the engineer menu.
Disconnect all HDMI sources from the inputs.
Unplug the power from TV/LCD for 10 minutes.
Plug the TV/LCD back in.
Connect the HDMI cable one device at a time.
Turn on the device (ex. PS3).
Repeat steps 4-5 for each HDMI port.
