The attached test program is a modified version of HelloJFXPanel with EXIT_ON_CLOSE replaced with DISPOSE_ON_CLOSE. This works fine on Windows and Mac, but fails on Linux with the following error:

The program '<unknown>' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadWindow (invalid Window parameter)'.
  (Details: serial 799 error_code 3 request_code 20 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

This failure happens with either the es2 pipe or the j2d pipe.