I have just set up my new ATV 4 with my universal IR remote (Don’t laugh. It controls everything very nicely 
). My IR remote is fully programmed using ATV setup guide. All buttons on the learned remote have been tested during movie playback and work fine.
I found either a GUI inconsistency or bug or both when using both the Apple remote or my IR remote.
I will do my best to describe it here.
After selecting a video to play the user is taken to video overview page with the play and edit buttons. Below that there is the horizontal thumbnails row of “recent” videos.
I CAN use use the apple tv remote to scroll thru the horizontal videos and press the “play” button to start the movie. The touch pad button on the ATV remote DOES NOT start the movie. It would be great if it did.
Now using the universal IR remote to carry out the same action to start a movie, the defined “play” button on the remote does nothing. This I believe is the bug. It only happens on “learned” remotes. It should work. The workaround is to scroll back up to the on screen PLAY button and press select to start the movie. This is very cumbersome.
The defined “select” button (touchpad button) on the learned remote also does nothing except select the movie. This is consistent with the apple remote however like I said above it seems more intuitive for the ‘select’ (touchpad button) to start the movie. You also have to do the work around to play the movie.
So basically there is a Bug and a GUI issue (IMHO). Both seem easy to fix.