Bug discovered and testcase supplied by Darryl Dixon, Winterhouse Consulting Ltd.
  1. Hover your mouse over this text (blue) to make the list below (pink) appear.
  2. Note that the bottom element of the list overlaps the iframe below.
  3. Move your mouse off this text and the list and notice that the list below disappears (good!).
  4. Hover again and then move your mouse down the list on to the iframe.
  5. Notice that the list doesn't go away (bad!).
  6. Move your mouse anywhere in the iframe.
  7. Notice that the list still doesn't go away.
  8. Move your mouse anywhere off the iframe and list.
  9. Notice that the list now goes away as the browser 'wakes up' and realises I'm not hovering over the list any more.
  10. A footnote: the elements don't actually have to be touching or overlapping to trigger this bug, it's just easier that way. In fact, if you simply move your mouse fast enough from the hovered element onto the iframe, even if they're not touching, the hovered element will continue to hover.