Explanation

In IE11, the display of a SELECT field can get out of sync with its internal scroll position.

Demonstration

  1. Click "option e" in the list.
  2. Click "Hide".
  3. Click "Show".
  4. Click "Scroll".
  5. Note that the list was scrolled with "option e" at the top.
  6. Click "option j" in the list.
  7. Click "Hide".
  8. Click "ShowAndScroll".
  9. Note that the list does not appear to be scrolled with "option j" at the top.
  10. Move the mouse over the list, and note that the highlighted option is out of sync with the mouse cursor position.
  11. Click the down arrow on the scroll bar.
  12. Note that the list jumped to the "correct" position instead of just scrolling one line, and now everything is normal again.