Shader selector button disappears on selecting shader with long path.

Steps to repro:
1. Create a new project.
2. Windows > Package Manager > Visual Effects Graph > Install.
3. Packages > Visual Effect Graph > Editor > Templates > Open Simple Static Mesh.
4. Change Shader in Static Mesh Output block to "Legacy Shaders/Transparent/Bumped Specular".

Actual Result:
Shader selector button disappears.

Expected Result:
Shader selector button does not disappear.

Reproducible in:
2019.3.0a12, 2019.3.0a10.

NOTE:
1. Visual Effects is introduced in 2019.3.0a10.
2. Could not test on Mac due to https://fogbugz.unity3d.com/f/cases/1174796/

Environment:
Only on Windows.