plugin or theme issue???

i have installed the events calender and and eventbrite for events calender plugins. they work, calender works and it generates tickets no problem, however, when i go to the eventbrite website and take the html for my ticket and add it to my post, the thumbnail image disappears off the home page/catagories etc, but still remains in the post itself. does anyone know if this is a problem with wp or theme or plugin or what?? thanks.