When images are referenced in the tooltip for a layer, the AJAX viewer with Internet Explorer can yield some very odd results. If it takes too long for the image to be returned, say more than 4 or 5 seconds, it's like it tries to call the image again and then this causes a loop which makes the tooltip to appear to blink. For an example that I just ran into, see http://mapguide.spatialgis.com/mapguide/spokanemaps/ and turn on the DOT Cameras layer. When you float your mouse over one of the camera symbols, a DOT traffic camera image should appear, but often times results in the above behavior. This works just fine in Firefox.