Scheduler jobs with twilight restriction are properly aborted when dawn approaches, but are re-evaluated and re-scheduled with no regard for said dawn, preventing the observatory from shutting down properly. This is a regression introduced by "1e299fdf5 - Fix parking engine, and make observatory startup job-centric".
The situation now is different. The Observatory does shut down, but a new job is started between the pre-dawn margin and the actual dawn limit.