How to reproduce:
1. Open the attached project named "enum_popup_repro" or create a new one
2. In player settings -> other settings set windows graphics API to OpenGLES2 or OpenGLES3 or OpenGLCore
3. Select Directional Light in the Hierarchy then collapse and expand the Light component in the Inspector
4. Select Type or Mode or Resolution enum popup in the Inspector
5. The light component will collapse when selecting an enum

Expected result: Component does not collapse
Actual result: Component collapses

Reproducible with: 2018.1.0a6, 2018.1.0b5, 2018.1.9f1, 2018.2.5f1
Not reproducible with: 2017.2.3p3, 2017.3.2f1, 2017.4.9f1, 2017.1.0a5, 2018.3.0a1, 2018.3.0a9

Note: Issue reproduces with any components enum popup. The issue sometimes takes a couple of tries to occur.