Repro steps:
1. Open the attached project in "test-1190042.zip"
2. Go to Assets > Scenes > SampleScene
3. Click on the Directional Light Game Object in the Hierarchy tab
4. Click on the arrow next to Capture Components under Alembic Exporter (Script) in the Inspector tab

Expected results: the drop-down menu is opened
Actual results: the drop-down menu is not opened

Reproducible with: 1.0.6 (2019.3.0a7, 2019.3.0b11, 2020.1.0a1, 2020.1.0a14), 1.0.0 (2019.3.0a7)
Not reproducible with: 1.0.6 (2019.2.0a1, 2019.2.13f1, 2019.3.0a1, 2018.4.0f1, 2018.4.13f1)
Unable to reproduce with: 2017.4.0f1, 2017.4.35f1 (not compatible with the Alembic Package)

Notes:
*Issue is only reproducible with the Alembic Exporter (Script) component
*The menu drops down after clicking on the title of the parameter