When hovering right below the black bar, the mouse.X and mouse.Y read to ignore the offset created by the topbar. This is nonstandard behavior and is not replicated in-game.
However, once you click, the mouse X and mouse Y will revert to standard behavior. As soon as you move the mouse again, it stops.
An example of the nonstandard behavior, where mouse.Y is ignoring the top-bar offset
This only happens in studio, and is inconsistent with what happens online.
When hovering right below the black bar, the mouse.X and mouse.Y read to ignore the offset created by the topbar. This is nonstandard behavior and is not replicated in-game.
However, once you click, the mouse X and mouse Y will revert to standard behavior. As soon as you move the mouse again, it stops.
An example of the nonstandard behavior, where mouse.Y is ignoring the top-bar offset
This only happens in studio, and is inconsistent with what happens online.