One more problem that I have with the File Chooser Dialog:

Here is the scenario:
1.) User clicks the 'Export' button. FileSaveService is called
Security Warning -> click 'OK'
FileChooser dialog appears
 Type in test.png and click 'Save'. a file is saved on the local filesystem

2.) User clicks again the 'Export' button after a file was saved
Security Warning -> click 'OK'
-> Result: File Chooser does _not_ start..nothing happens