Steps to reproduce:
1. Create a new project
2. Create a custom package folder in Packages
3. Drag a gameobject into the package folder through the project window

Expected result: gamobject instantly appears as an asset in the project window
Actual result: this action does not refresh Asset Database and thus it does not appear until you manually refresh

Reproduced on 2018.3.0a6, 2018.3.0b11, 2019.1.0a10
Not reproduced on 2018.3.0a5
Regression introduced in 2018.3.0a6(introduction of new prefabs)

Verified FIXED 2018.3.2f1, 2019.1.0a13