Reproduction steps:
1. Open the attached project
2. Open the "mainscene" scene
3. Set the main camera to orthographic, enable the attached Raycaster2D component, and disable the BetterRaycaster2D component
4. Enter play mode
5. In the game view hover your mouse cursor over the yellow sprite
--- You mouse over the sprite, you get a message in the Console
6. Exit play mode
7. Change the sprite's z-coordinate to -20
--- Which puts it behind the camera and out of view
7. Enter play mode
8. Mouse over where the sprite used to be
--- Note the console says the sprite is being moused over. This should not happen.

User suggested a fix:
The offending Unity code, as found at https://bitbucket.org/Unity-Technologies/ui/src/fadfa14d2a5cb8d6462db067e669b4b2bc11a018/UnityEngine.UI/EventSystem/Raycasters/Physics2DRaycaster.cs?at=4.6
var hits = Physics2D.RaycastAll(ray.origin, ray.direction, dist, finalEventMask);
They propose changing that to:
var hits = Physics2D.GetRayIntersectionAll(ray, dist, finalEventMask);

This change also fixes case 734723