oops, not quite sorted.
I noticed that the proposed fix, in setting the ul#cssmw li attribute from relative to static causes another issue.
With this in place, the submenus no longer work, and when you mouseover the nav bar, instead of the submenu, a scrollbar appears on the right
Alternatively
...Could an alternative 'solution' be to change the position of the datepicker relative to the text field being edited ?
By default it seems to appear below the field. If the field is near the bottom of the page, the datepicker appears above.
Is it possible to force it to the side ?