The question is why are you making Widescreen Bars? There is no need to ever do this. If your content is widescreen but you need to deliver it in standard 4:3 ratio, you do this at rendering time, not editing time. That's your problem.
Change your project to widescreen and render to 4:3 and let Vegas add the widescreen bars for you. Then none of the transitions will ever have a chance to mess this up.
~jr
http://www.johnrofrano.com
http://www.vasst.com