Event "dialog:beforeclose" not always triggered when closing a dialog

When closing a modal by clicking the "X" in the top right the "dialog:beforeclose" event is not triggered.

I could be wrong but this is what I think is happening.

The only place the "dialog:beforeclose" event is triggered is in closeDialog() but this not called when closing the modal in this way.

I found this when working on #2830882-45: Introduce Drupal.offCanvas, mirrored after Drupal.dialog, to avoid Settings Tray using Drupal.Dialog in unintended ways
Firing all the events in the dialog cycle would be necessary to make Bootstrap compatible with this.