Comment 7 for bug 649441

Currently, (as of r13276) the behaviour is this:

Unless "Live Preview" is checked, the dialog is non-modal. But ifLive preview is turned on, the dialog becomes modal.

The issue with this is because on newer GTK versions, the modal dialog greys out the rest of the screen, and centers the dialog in the middle of the screen. Most times this covers the output of the live preview, and essentially makes it useless. (screencast attached)