I had the drop down menu setup as a mega menu. Recently I was on the site and noticed that the mega menu is acting very strangely in that the first level appears when you mouse over the top level but the third tier only appears when you mouse over the second tier.
Also I noticed that the drop down under the “About” is off to the left when it should be right aligned.
I looked in the additional css in the “Customise” section and it seems to be blank, but I am pretty sure that I included the drop down css in there. I did an update recently (cant remember when), but thinking that may have had something to do with it.