That is a nice looking drop you have there.
Would love to see it when you’re done.
Have you tried placing the dropdownlist inside another div / wrapper.
Not sure if it will solve the issue…
but I’ve been working on a megamenu that does something similar…
to what you appear to be doing…
except with images, checkboxes and input fields.
I think either @vincent or @danro has something similar as well.