Custom menu stretching during drag & drop

I’ve encountered an unusual problem with the Custom Menus:
When I try to drag & drop an item, the menu starts running up item spaces down the page. It’s not just that the function doesn’t respond (as in other posts I’ve read), but it has this strange behavior.

Here’s a link to better illustrate what happens when you try to move an item in any direction.

http://www.clintondrug.com/wp-content/uploads/2013/11/custom-menu.jpg

I’ve already disabled ALL the plugins & tested on other pc’s & browsers. Same results.

Any help is appreciated!