User Event Script - Trigger on 'Mark as Packed'

I have a User Event script on the Item Fulfilment record - set to run on all roles, all contexts, run as Administrator.

The script has different functions for 'type == 'edit' and type == 'create'

These work as expected when a Fulfilment is created or edited in the UI

Some of the function are reliant on the Status of the fulfilment. The script runs after submit, so if I edit a Fulfilment, set the Status to Packed (in the drop down) then save the Fulfilment, the script processes as expected (based on the Status being Packed).

However, if the Fulfilment is Picked, and I use the 'Mark as Packed' button, then the script doesn't appear to trigger. In the System notes the status change appears under the context of UI - so I'm not sure why this isn't triggering?