It should at least show an error message for images it cant load. Are you sure you have clicked the preview and then scrolled the page to the top? (the preview result is shown at the top of the page).
You are so right, the preview is at the top -- I was just used to StackOverflow style of in-place preview
The difference between StackOverflow and Bitcointalk is -- Bitcointalk never closes my question, and I'm so impressed and grateful to this community