Reproduction steps:
1. Open the attached project "Testing.zip";
2. Open the Test scene;
3. Select the Cube game object in the Hierarchy;
4. Enter a play mode.
5. Observe the results of the field "Number of Collisions".

Expected results: there should be shown only collisions of the objects on the specific layer (on the attached project there should be value 1).
Actual results: the parameter shows the number of all collisions (on the attached project value is 2).

Reproduced on: 5.5.0f3, 5.6.0b10, 5.6.0f1, 2017.1.0a3. (shown value is 2)
Not reproduced on: 5.4.4p3. (shown value is 1)