There are a couple issues with JProgressBars under GTK L&F that make them look different
than native GTK progress bars (first reported in umbrella bug 6417110):

  1) Vertical JProgressBars paint the foreground incorrectly; this is most visible
     on themes like Human and Clearlooks that use a gradient.

  2) The preferred width of vertical JProgressBars differs from their native
     equivalents.

Use the attached JavaWidgetFactory testcase to compare against the native behavior
in the attached "twf" application.