Steps to reproduce:

1. Open attached project
2. Open scene "2D-RAT"
3. Run scene
4. Player will fall until it collides with platform
5. Notice that once collision happens "I'm in air" is still getting printed. This means that LineCast between player position and point bellow his feet couldn't detect ground in between

Additional steps:
6. Press "D" and space couple of times to jump on platform on the right
7. Notice that this time player gets grounded

Reproduced with: 5.6.0p2, 5.6.1p2, 2017.1.0b6, 2017.2.0a1
Not reproducible: 5.6.0f3