I perform some further testing this afternoon.
I played a High School Musical BD (with pop-up menu ON) for 20 mins, then I switch to another source (my DVD player). No matter what I am playing, or even I pressed STOP on DVD player - I can still see a shadow/retented image of HSM3 on my LCD TV. This only happen in HDMI channel (which my LCD has only 1 HDMI input), does not occur in component, S-video, or TV channels.
The shadow lasted for quite long, at least for this recent experiment - it is over an hour. My LCD was Acer 37" 1080p LCD TV bought in 2005.
I tried to unplug the power of the HDMI switch for a few minutes, and upon plugged back in, the shadow is still here.
I also tried to unplug the HDMI cable from the HDMI switch, and connect it directly to my DVD player. Same thing (shadow is there).