The font doesn't change the second time on selecting a different font asset.

Steps to repro:
1. Create a new Project.
2. Gameobject > 3D Object > TextMeshPro - Text.
3. Click on "Import TMP Essentials".
4. Click on "Import TMP Examples & Extras".
4. In the Inspector, under Main Settings > Font Asset
5. Open Asset selector window > Select "Antom SDF" asset.
6. Select other assets.

Actual result:
The font doesn't change the second time on selecting a different font asset.

Expected Result:
The Font should change for each and every asset selection.

Reproducible in:
2019.1.0a10.

Working Fine In:
2019.1.0a9, 2018.3.0b12.

Environment:
Windows & Mac.