When the signal disappears from an active HDMI port, the TV will by default go back to the "always on" connection, which is the Tuner input. To avoid this, you could change the input prior to powering down the player.
I have a Samsung HT-BD1250 Blu-ray Home Theater System connected to a Samsung LN52A650. I also have an ATT Uverse cable box connected to the tv via the other HDMI input. Ok so I am watching TV with my cable box and I want to watch a movie. I decide to turn on the Blu-Ray player and the tv automatically switches to the input from the Blu-Ray player and plays the movie as usual. Once I am finished with the movie, I power off the Blu-ray player and the tv goes to my over the air(antenna)input instead going back to the cable box hdmi input. Can anybody tell me how to fix this? It's pretty frustrating having to switch the input back to the cable box every time I use the Blu-Ray player.