Steps to reproduce:

1) Download attached project 'RenderTextureBug-5.6.0.zip' and open in Unity
2) Open scene 'Test' and press Play
3) Click on the Test button and check the Console window

Expected result: Value for the front should be 387 and for the back 6124 (check attached image 'expectedOutcome.png')
Actual result: Value for the front is 375 and for the back 6061 (check attached image 'actualOutcome.png')

Reproduced with:
5.6.0p4, 5.6.3p2, 2017.1.1f1, 2017.2.0b10, 2017.3.0a7

Not reproduced with:
5.6.0a1, 5.6.0p3

Regression since:
5.6.0p4