How to reproduce:
1. Open the attached project "TexStreamTest.zip" and scene "SampleScene"
2. Enter Play Mode
3. Exit Play Mode
4. Zoom out in the Scene view such that the Game View objects are small inside the Scene View
5. Hover the mouse over the Game View

Expected result: Game View remains the same
Actual result: all Game View texture quality changes to the mipmap levels used by the Scene View

Reproducible with: 2019.1.0a13, 2019.1.0b9, 2019.2.0a10
Not reproducible with: 2018.3.0a6, 2018.3.23.11f1, 2019.1.0a1, 2019.1.0a12
Could not test with: 2017.4.24f1 (no texture streaming), 2018.3.0a5 (the repro project's prefabs break due to unavailability of nested prefabs)

Note: it is necessary to enter Play Mode only to make the script "ShowTextureStreamingSummary.cs" which is attached to the "MainCamera" run