I've never heard of that happening, but it must be something CEC related. In either your TV settings or the Roku settings, disable CEC. On the Roku, it's likely under System/Control Other Devices. Depending on the player, it might just say 1-touch play, or actually have a CEC function listed. Just turn it off.
Of course, it could be a defective remote for the TV, and whatever button you are pressing might be sending an input change signal instead of its intended purpose.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.