Unfortunately, that is probably the fault of the TV manufacturer.
Google gave them the source to add Chromecast to their device and it appears that a lot of TV makers modified that. Especially when it comes to Ambient Mode. We get a lot of reports from people that have NO control over Ambient Mode on their chromecast-built-in devices.
I would suggest you contact the maker of your TV. They, hopefully, can tell you if this is a limitation they introduced or if it is a bug they intent to fix.
