In IE Win, the menu items jump around. When the page is loaded the items are two pixels to the left of where they should be. Hovering over a link makes the link jump to the correct place. If there is a line without a link above it (like the "Shortitle"), it also fixes the line. However if a line has no link just below it (like the first part of the "Longer_title like_this"), its position can't be fixed.
jkd

The first submenu has the text correctly placed.

The second is two pixels off to the left.

The third is four pixels off.

The complexity of the menu doesn't matter. If the long one is put first it is the same. Each new submenu is off two more pixels.

Removing the left border of the submenu fixes the problem. Trouble is, I need that border...

Adding a white (invisible) border to the right and bottom of the submenu also fixes the problem. Eureka!!!!