UI Transitions for 'Highlighted' break unless you have your UI on the UI layer.
Did some experimenting before wanting to post this and this is what i've found:
If your UI is on the Default layer, the transition for 'Highlighted' will not work for sprite swap, Animation and Color tint.
If your UI is on the UI layer it works as expected as long as you have your menu open.
While this is pretty minor it can inhibit the creation of accessibility tooltips for buttons and can potentially be a mechanical gate for desktop users on maps that decide to use the Animation on Highlight as a mechanic to progress through the map.
The Animation button shows how this can be used as a mechanical tool, I have a cube that permanently turns on when the animated cube turns on when you hover over the button.
The Sprite Swap button changes sprites on hover.
Color tint is your usual UI button that tints it's color on hover.
This is the world I did the testing in, has UI buttons with all 3 types on both layers: