What steps will reproduce the problem?

1. Start DFO for the very first time.
2. Select and deselect each of the Edited and Commented Search items

What is the expected output? What do you see instead?

Because there are no photos, I'd expect nothing to happen. Instead, the program crashes with:

Exception in Gtk# callback delegate Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception. System.NullReferenceException: A null value was found where an object instance was required. at DeskFlickrUI+<>c__CompilerGenerated2.<>c__AnonymousMethod33 (System.Object +5, System.EventArgs +6) [0x00000] at Gtk.Application+InvokeCB.Invoke () [0x00000] at GLib.Timeout+TimeoutProxy.Handler () [0x00000] at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal) at GLib.Timeout+TimeoutProxy.Handler() at GLib.Timeout+TimeoutProxy.Handler() at Gtk.Application.gtk_main() at Gtk.Application.gtk_main() at Gtk.Application.Run() at DeskFlickrUI.CreateGUI() at GladeApp.Main(System.String[] args)

What version of the product are you using? On what operating system?

0.7+svn45-1 on Debian.

Later...

Now that I have photos, I see that selecting and unselecting these checkboxes does not cause the crash.

Thanks for this bug report. Its fixed now.