Custom Editor window closes when using Object Picker and the object field doesn't change after selecting a different object.

How to reproduce:
1. Open the attached project "BlockSampleDLKPromotion.zip"
2. In the Project window - select MyAssets > DLK > LoadingPatternRepositories > TerrainTestRepository
3. Click "Edit Repository" in the Inspector window
4. In the custom window, that has appeared, click on the "Miniature Map Asset Creator" Object Picker

Expected result: custom Editor window doesn't close and the object successfully changes
Actual result: custom Editor window closes and the object doesn't change

Reproducible with: 2020.3.13f1, 2021.1.14f1
Could not test with: 2018.4.36f1, 2019.4.28f1, 2021.2.0b2, 2022.1.0a1 (Custom window doesn't open due to errors)

Notes:
- Dragging an object from the Project window to the object field successfully changes the field