I have the 4K Fire TV and the HDHR. I just installed the channels app.
What I notice is that when hitting the return button on the remote, sometimes the last frame is left on the screen ghosted over the menu. Choosing another channel does not help, in that the last frame from the last channel is still superimposed.
To fix it I have to switch to a different HDMI input, which clears the screen, then go back to the FireTV.
Is there some other way to change channels? Is there something I should do before pushing the return button? I will have to experiment.
I have an Epson 4K projector.
The problem never occurs with the HDHR app, but it has an audio issue, which is not for here.