Last modified: 2014-09-22 14:45:27 UTC
That's because the event is emitted by the parent method (Window#close), which is called with a delay of 250ms. Talked to Trevor, reporting on bugzilla just to keep track of it.
This seems to have been fixed, perhaps in the great and terrible dialog refactor (3ba36b9a53aa41da07c3b56a063fe0d3c419c2a5). It has definitely become irrelevant since Windows, and this Dialogs, no longer emit any events anymore.