UI1.5b4 Dialog Modal Broken

UI Release 1.5b4 Dialog, when setting modal: true, results in the following error in Firebug:

dialog.options has no properties

create(Window jquery_ui_dialog_tut.html)ui.dialog.js (line 346)

overlay(Window jquery_ui_dialog_tut.html)ui.dialog.js (line 298)

open()ui.dialog.js (line 222)

(no name)()ui.core.js (line 125)

each([div#dialogTest.flora], function(), undefined)jquery-1.2.4b.js (line 742)

each(function(), undefined)jquery-1.2.4b.js (line 140)

(no name)("open", undefined)ui.core.js (line 120)

(no name)()jquery_ui_dialog_... (line 28)

handle(Object originalEvent=Event click which=1 view=window)jquery-1.2.4b.js (line 2076)

(no name)()jquery-1.2.4b.js (line 1859)

[Break on this error] }, dialog.options.overlay));

Removing modal everything works fine. This occurs with jQuery 1.2.3 and 1.2.4b