Steps to reproduce:
1. Open the attached project (RenderTextureGrabPassRepro.zip)
2. Open the Assets/main.unity scene
3. Observe the error in the Console window
Assertion failed on expression: 'entry->m_Rect.height == height

Expected result: Error should not appear in the Console window
Actual result: Error appears in the Console window

Note:
I was unable to test with 5.3
Camera's (RenderTextureCamera) viewport rect is changed from the default values
Cubes Z position is set to 5.5f

Reproduced with: 5.4.4p2, 5.5.0f3, 5.5.1f1, 5.6.0a1, 5.6.0b4, 5.6.0b6