Repro steps:
1. Open attached project
2. Open scene "SampleScene"
3. Set the Aspect Ratio to 4:3
4. Enter Play Mode
5. Select the "New Render Texture" in the Project Window to see the texture in the Inspector
6. Return focus to the Game View and press A
7. Observe the texture and press A again

Expected: the Texture fills up the RenderTexture after the first press of A
Actual: You need to press A two times for the Texture to fill the RenderTexture

Reproducible with: 2017.2.3p4, 2017.4.10f1, 2018.1.9f2, 2018.2.6f1, 2018.3.0a10