Testing this I discovered that using some of the "built-in" screensavers resulted in the dysfunctional behavior you described (and worse, it would attempt to install random channels as well after returning to Home) after pushing play/pause.
The following screensavers exhibited the Home/loading other app behavior upon pressing the PLAY/PAUSE button when activated:
Don't use: Roku City Stroll/Movie Magic, Roku Space, Roku Western, Roku Kids, Roku Nautical, Roku Jungle
The following screensavers functioned normally upon pressing the PLAY/PAUSE button when activated:
Use: Roku Digital Clock, Roku Analog Clock, Roku 4K Screensaver, Star Trek Theme Screensaver, Roku Skyline, Roku Aquatic Life (both versions), Roku Logo Rain
(Roku Mobile Screensaver simply locked the Roku up entirely when previewed/set)
So, for now, use a screensaver listed in the second group.
As well, please fill out a bug report:
https://support.roku.com/contactus/contact-options