Accordingly to spec. for FileDialog - http://docs.oracle.com/javase/8/docs/api/java/awt/FileDialog.html
"since it is a modal dialog, when the application calls its show method to display the dialog, it blocks the rest of the application until the user has chosen a file."

Please run the attached test and push 'Open' button. A file dialog will appear. Try to push 'Close' button on the parent dialog - you cannot do that because it is blocked.
Close the tests.

Then change parent of fd to null:
FileDialog fd = new FileDialog((Dialog) null);
- now you can close the parent dialog before the FileDialog - that seems to be a bug; and application is still running even after closing both of the dialogs.

If change 'TOOLKIT_MODAL' to any other modality type then the parent dialog should be blocked again.

Checked with JDK9-b14 on Ubuntu 14.04 Linux and Windows 7.