How to reproduce:
1. Open "BugRepro" Unity project
2. Enter "Test" scene
3. In the hierarchy select "gameobject"
4. In public variables "b" and "d' fields type letters : "e", "t", "y", "i", "a", "f', "n"

Expected result: b field is float type and c field is double type, so it should only accept numbers
Actual result: it accepts letters "etyiafn"

Reproducible with: 2018.2.0b1, 2018.1.0f1, 2017.4.1f1, 2017.3.2f1,2017.2.2p2, 2017.1.3p2