When sprites are imported "Alpha is Transparency" is disabled. If a user selects "Editor GUI " or "Sprite" under Texture Type and then back to "Default" the "Alpha is Transparency" is now enabled.

Expected:
The "Alpha is Transparency" should not be enabled on default texture type.

Steps to reproduce
- Select 2D Artwork > PNG > Bomb Sprite
- In the Inspector "Alpha Is Transparency" is disabled.
- In the Texture Type select Editor and then select Default
Notice issue >> Alpha is Transparency is now enabled. The Revert and Apply buttons are enabled.

Broken: 2018.3.3f1, 2018.1.9f2
Working: 2017.4.17f1, 2019.1.0a14