Procedure to reproduce: 1) Visit http://www.ncix.com/ 2) Wait for page to load 3) Move the mouse rapidly enough over the left hand side column so that the browser doesn't have enough time to load the new mouseover'd image before you move the pointer away. The entire list disappears as the layout engine appears to collapse the table as the images are not loaded, and leaving the link doesn't cause the original image to redisplay. Pausing long enough to let the image load avoids the problem.
Dupe of Bug 32269?
*** This bug has been marked as a duplicate of 32269 ***