Reproduction steps:
1. Open the attached project;
3. Open the scene "main";
3. Enter Play mode;
4. Press "Space" key;

Actual result: the sphere goes on the capsule.
Expected result: the sphere should stay where it is.

Note: If you disable "Render Target Set" script in an object "Camera 3", everything will work correctly. The problem happens because of targetTexture is set to null and when this function is set at least on two Cameras.

Reproduced with: 5.6.0a1, 5.6.0f1, 2017.1.0a6
Not reproducible with: 5.4.5p1, 5.5.0b1, 5.5.3f1
Regression introduced in 5.6 alpha

Note#2: verified with 5.6.1p1 version