No problem....here is the play by play:
Launch theater view (I use Xplain's Rapier Fusion theme if that makes a difference), anyway get Theater View home screen
Point mouse at horizontal roller bar (in my system this is PLAYING NOW, MOVIES, WEATHER, NEWS ..[snip].. EXIT)
Use finger to move mouse roller wheel, expected reaction is roller bar of menu items moves right, stop wheeling when mouse points to item I'm interested in lets say NEWS
....[read news], click BACK button on mouse get back to home screen
Use finger to move mouse roller wheel to item I'm interested in lets say PLAYING NOW, click, ...[etc, etc]
On system A, v18.0.9x roller bar doesn't move but did for years with releases prior to 18.0.90 (mouse is wired Logitech G500)
On system B, v18.0.84 roller bar moves horizontally right/left as described above (I reverted from v18.0.90 to v18.0.84 to get behavior back, mouse is Microsoft wireless mouse)
Key take aways are A) home screen roller bar is what I use 98% of the time and the horizontal behavior disappeared in some build 18.0.85 or newer. B) mouse brand (mouse driver?) doesn't matter, and C) re-installing build 18.0.84 brings functionality back. Note - I am not depressing mouse roller wheel, just rolling it. Same behavior I would use to scroll text in a browser window.
FastKayak / Larry