You can turn off Anynet+, as that's what it doing this. You may think this is a setting you can change. Unfortunately, it's not. Either you can turn Anynet+ on with all of its functions with this switching away, or you can turn Anynet+ off and stop having it switch away at start up.
I have a HT-E5550 home theater system connected to my 7500 series TV. My STB is connected to the HDMI 1 IN on the HT-5550. Every time I switch on the HT-5550 it remembers that the HDMI 1 was selected, for about 5 seconds, then it drops it and displays a "Select input source" screen. Then I have to step through the input sources until I get to the HDMI 1 agin. After that it keeps the input source, until next time...
Any clever ideas why and how to fix this?