Steps to reproduce:

1. Create new project
2. Set full screen mode to Exclusive
3. Build and run 800x480 windowed player
4. Hold alt and quickly tap <enter> twice
5. Once player is windowed again notice that window size is a bit larger than before step 4

Repeating step 4 will make window increase in size until it takes up whole screen

Reproduced with: Version 2017.2.0a4 (6c5608f3defc)
Thu, 15 Jun 2017 13:04:07 GMT
Branch: se/platform/windows-fixes

Doesn't reproduced: 5.5.3p4, 5.6.1p4
Can't test on 2017.1/2017.2 as there window is instantly maximized after exiting fullscreen