1. Create and save several scenes in your project
2. Add them into 'Scenes in Build' list in any order (go File -> Build Settings)
3. From Asset store import any package that has scenes inside. E.g. 'Shooter Kit - Halloween Range'
4. Review 'Scenes in Build' list

Actual result:
All previously selected and ordered scenes are removed from 'Scenes in Build' list. Scenes of the imported package are placed there instead, although user didn`t mean that

Tested on:
5.2.4f1 - not reproducible
5.3.3p2 - reproducible
5.4.0b7 - reproducible