How to reproduce:
1. Open given Unity project
2. Enter "Main" scene
3. Enlarge circle to 400 for a better result
4. Enter Play Mode
5. Hover the mouse button over the white circle

Expected result: The collide between mouse cursor and circle should be more accurate
Actual result: When hovering not over the circle, the mouse cursor is changed sometimes

Reproducible with: 2018.2.0a5, 2018.1.0b11, 2017.3.1p4, 2017.2.2p1, 2017.1.3p2, 5.6.5p3

Note: this bug only happens when the game window is anchored in the main unity window, the mouse y axis origin is slightly lower than the bottom of the window, so the y mouse position is always a few pixels higher than it should be. If you pop the window out of the main window, the bug no longer appears.