First let me say, I'm using Tigra Menu Gold, and it is awesome. That said, now on to my issue.
It seems like my dropdown menus have a small 'gap' at the bottom of each cell and when I hover over this 'gap' the menu retracts to it's normal form. This 'gap' only seems to be at the bottom of each sub-menu item and the top portion of each sub-menu item seems to hold the menu in place just fine.
I am also having the same problem and it is driving me nuts, the only way i see to fix it is to overlap my menus more but from a design standpoint it
just doesn't look good.
I will poke around and see what I can find.
The best way I have found to work around this problem is to make the menu's base size bigger and then to overlap them. Unfortunately the last item tends to have a bigger box than I want but it works.
Feel free to submit a support ticket attaching your page with the menu, we'll check it out and suggest some nice'n'elegant way around.