I'm trying to program an automation rule that is set to trigger when a ticket with a specific label is transitioned into a specific status (called "Ongoing" on my board), and it will then change the Due Date automatically to the start of the week in 2 weeks (i.e., using {{startOfWeek(2)}} to do this), and reduce priority. The attached screenshots shows how the automation rule is configured.

According to the audit log, the rule succeeds when triggered. However, the Due Date field of the transitioned ticket is cleared. This means that no due date is displayed in the ticket's Due Date field (where, for example, it was set to today's date prior to the transition). Meanwhile, the Priority is indeed changed as expected.
Can somebody tell me if I am missing something, or if I happened on buggy behavior?