Sprite Atlas is incorrectly packing sprites with alpha into RGB format

1. Put attached sprite into Assets folder
2. In Assets, right click > Create > Sprite Atlas
3. Using Default settings (Compression None), drag the sprite into the atlas for packing
4. Pack Preview

The resulting format should be RGBA, not RGB.

Occurring on: 2018.1.0a4, 2017.3.0b8 - b1
Not occurring: 2017.3.0a7, 2017.3.0a1, 2017.2.0f3