A timer job's schedule type is changed from yearly to hourly after running it

Hello.

A timer job's schedule type is changed from yearly to hourly after running it on SharePoint Server 2019.

How can I prevent this?

I have a custom timer job with a yearly schedule (SPYearlySchedule). After I deploy it, its Schedule Type listed under Job Definitions in Central Admin is shown as Yearly as expected. However, if I manually run this timer job (by clicking "Run Now"), the Schedule Type for the job is immediately changed to Hourly - and indeed the job will run every hour after this, instead of every year.

With best regards, Vasily