There are some elements that overlap the tooltips, such as select form elements and flash animations. DOM Tooltip can hunt down and hide these elements that cannot be overlapped.* The solution is somewhat crude, but necessary in order to ensure the tooltip remains visible.
Note: The collection of elements to hide is cached in a variable domLib_collisionElements on the first tooltip activation. It is possible to flush the cache and force a new search by setting the global variable domLib_collisionsCached to false.
* This problem is very browser specific. In IE, select elements are drawn using the native window library widgets and are thus sitting on top of the html page layer. Therefore, no html element can go above these decorations.