Steps to reproduce:

1. Download the attached project (ForceStopIssue) and open SampleScene
2. Navigate to the Lighting Settings and make sure that Auto Generate is disabled
3. Generate lighting
4. Once the baking initiates press Force Stop button
5. Notice that the operation either takes a very long time to finish or does not finish at all

Notes:

- Cancel button still works
- The amount of time for the Force Stop operation to finish increases proportionally with a number of lightmaps in flight
- Reproducible both on Mac and Windows