"Valid to" is extended when create new Validity Period using App Manage Activity Types

You use App Manage Activity Types to extend Validity Period for existing Activity Type.

Example:

However after you created above new Validity Period, you find row 2 and row 3 are combined into one Validity Period.
This happens also if you use API API_COSTCNTRACTIVITYTYPE_CRUD_SRV (SAP_COM_0357) to create the new Validity Period.