Steps to reproduce:
1. Open attached project "touch"
2. Open "test" scene
3. Build and run the project on windows (windowed mode)
4. Notice that if you touch on the screen and drag it out of the (game)window and release it, Unity still thinks finger is being pressed

Reproduced with: 5.4.0b20

Not reproducible with: 5.3.1f1

Only reproducible on Windows. Not reproduced on iOS or Android.

Note: in order to reproduce you have to use a touch screen laptop/monitor. For this test I was using Lenovo Yoga 2 Pro.