ticket.submit.done event doesn't work if "Close Tab" is selected

I'm trying to use the “ticket.submit.done” event. This works if, when submitting the ticket, “Stay on ticket” is selected. However if “Close tab” is selected, the tab is closed before the event listener can run, so it doesn't work.

I have to use the “ticket.submit.done” function because I am trying to save some data back to a custom field, and there are other required fields that must be set before data can be written to the custom field. If I try and write data to the custom field before the ticket has been saved, and one of the other required fields has not yet been set, the update fails with a validation error (even though I'm not trying to write to that specific field).  

Does anyone have any suggestions of ways to solve this?