How to reproduce:
1. Download attached project file and open "main" Scene
2. Build Game
3. Select Fastest Quality settings and run game
4. Change game quality with PageUp button from fastest to Simple, Good, or Beautiful, or Fantastic (PageDown button drop-down quality)

Expected result: Frame rate should be 60FPS and 30FPS with "Every Second V Blank"
Actual result: Frame rate grows up to 500 and more

Reproduced with: 5.6.3p4, 2017.1.1p3, 2017.2.0f1, 2017.3.0b2

Note:
Application.targetFrameRate is set to 60;
Not reproducible if you launch game with Simple, Good, or Beautiful, or Fantastic quality settings;
Not reproducible in Editor; Not reproducible with MAC;
Tested on Win 10;