How to reproduce:
1. Download attached project file and open "Main" Scene
2. Enter play mode (Notice the console log for every frame)
3. Pause play mode and do not move your cursor or press any key (Notice the console does not log anymore)
4. Move your cursor in and out of the game view or move a game object to force the editor to update (Notice the console log each time the editor updates)

Actual result: When play mode is paused in the editor, coroutines are advanced each time the editor updates.

Reproduced with: 5.5.4p3, 5.6.3p3, 2017.1.1p1, 2017.2.0b11(#2), 2017.3.0a7