Assignment category is creating a new life event while hiring an employee

We are hiring an new employee. While hiring we are providing assignment category details as full-time.

This is triggering two life events one for new hire and other for assignment category change.

Same issue is happening in oracle demo.

For new hire, only New hire life event should be created.

We have verfied working hours change but it is not getting triggered while hiring an employee. Any reasons behind this?

Setup:

Data Change: PER_ALL_ASSIGNMENTS_M , EMPLOYMENT_CATEGORY COLUMN.

Any value to any value.

Any help on this is much appreciated.

Thanks,

Jahanavi