Scribe Upfront Dropdown Menu Splits on Click

Thanks in advance...
When a link at any level is clicked on the top navigation menu, the menu "splits" into its dropdown levels and freezes in that state for a second or two - displaying a menu "broken" into its different parts.
The site is on a reliable, fast host, plenty of bandwidth and I'm viewing it on a new MacBook, all the usual up-to-date browsers, with a high speed cable connection. I have not seen this problem on any other sites...

- Steph