Setup with a Toshiba tv, and everything works fine (all buttons) on the remote for the first 30 seconds, then you cannot adjust the volume on the tv or turn it off, it will only turn off the chromecast. Now the really odd thing is it will stop the tv remote working as well, so the only way to turn off the tv is to switch it off at the wall and you cannot adjust the volume at all.
I am tempted to throw it in a draw and put the old chromecast back on, as it all works.
Normally Chromecast should use TV CEC settings. If everything is adjusted correctly, then you can use both TV and Chromecast remote controller to change volume and switch on and off TV and Chromeact at the same moment with one remote controller only. Still you should have a possibility to use both remotes.
Start the process with each setting off.
Waht you can chec is to have a look at TV CEC settings (sometimes named differently by the producer) and Chromecast settings. My advice would be to not make all settings "on". Just try to do it one by one. Check effects each time you change the settings.