i too have this problem with an apex dvd and i think it is when you have your dvd player connected to the tv with a scart lead as soon as you power on the dvd the tv automatically goes to the dvd channel,and will then only accept signals through the scart lead. when you put your dvd into standby the tv will still only accept signals through the dvd scart lead and nothing else .to get the tv back to normal channels you have to physically turn the dvd off this is not a fault it is the way the tvs are set to go to a scart operated channel whenever power comes through them
hope this helps