How to reproduce:
1. Open attached project "InputTests.zip" (or create a new project and import Input System package)
2. In Project window, right-click -> Create -> Input Actions
3. Open newly created Input Action
4. In Input Action window, create ~6 "Action Maps"
5. Try to reorder action map 2 with action map 3

Expected result: the action map switch places
Actual result: the action map 2 goes down to the bottom of the list, an error is thrown "Should have drop target"

Reproducible with: 2019.1.14f1 (0.2.6, 0.2.10, 0.9.0), 2019.3.7f1, 2020.1.0b3, 2020.2.0a4 (1.0.0-prev.6)
Not reproducible with: 2018.4.20f1, 2019.1.14f1 (0.2.1)
Could not test with: 2017.4 (New Input System was not yet implemented)