This relates to a question asked here http://wordpress.org/support/topic/245516
At first we thought it was a issue with a slideshow plugin we added.
I am starting here this since it is related to the theme rather than the plugin.
A member provided the following analysis. Since we did not have the skill to find the problem. (see link above)
The problem is related to the z-index order. The part of the slideshow box that overlaps the dropdown menu is displaying with a higher z-index order than the dropdown menu, thus it gets priority and displays as the top layer where they overlap.
I have found a z-index hack for Safari in the .css sheet, it is set at "1" (thanks Jorn for the good commenting of the style sheet) when I change it to a higher number, the menu still does not come to the top and go over items added to the header or items in the sidebar.
I think this occurred on the 2.7 update. Running Dkret3 2.3 through 2.5.2 with 2.71 we have the problem.
Any ideas for a fix?