DropFilesEvent not working?

I read in the V9.0 release note that vtkRenderWindow now supports a DropFilesEvent that should allow me to get the names of the files that are dropped.

However, when I add an Observer to my render window and then drop files onto it, this event never fires?

I changed my observer to listen to AnyEvent and then print eth event name - but the DropFilesEvent never fires

Has anyone ever seen this working?

Indeed, it was fixed before 9.3.0.