To reproduce:
1. Open attached project
2. Open the scene "Scene"
3. Open the asset "WaterTexture_RT" in the folder "Art"
4. Set the Color Format to ARGB4444
5. Notice that the texture is drawn on the scene view toolbar
User has also attached a video explaining the issue.

Note: This only happens with ARGB444 on my machine, but for the user it's also reproducible with RGB565. No other color formats displayed such behavior.
Also note that this doesn't happen when in play mode.

Reproduced on: 5.5.0b3, 5.4.1p1, 5.3.6p5