Reproduction step:
1. Create new project and open Unity
2. Select Edit -> Project Settings -> Player
3. Check property Resizable Window
4. Build & Run

Expected: placing cursor on the edge of the built game's window would change the cursor's appearance (indicating possibility to resize the window)
Actual: placing cursor on the edge of the built game's window does not change the cursor's appearance

Reproduced on: 2017.2.0p1; 2017.2.1p1; 2017.3.0p1; 2018.1.0b1
Not reproduced on: 2017.1.3f1; 2017.2.0a1; 2017.2.0f3
Regression introduced: 2017.2.0p1

Note:
After collapsing the window and selecting it again makes cursor work as expected.