Import preview window doesn't resize after maximizing it to the limit

Steps to Reproduce:
1. Create a new project
2. Import any asset
3. Select imported asset
4. Drag import preview window vertically to the limit from inspector window
5. Drag it down to minimize.

Actually Result:
Import preview is not resizable after maximizing it to the limit

Expected Result:
Import preview should be resizable.

Reproducible on:
2019.1.0a10

Works on:
2019.1.0a9, 2018.3.0b12

Environment:
Windows and Mac

Note:
1. Refer attached video