Must use Boost theme.
Open an assignment with submissions.
Click View Submissions.
On the top of the page, Click the drop down box labeled: "Grading actions"
Click "Download all submissions"
The download box will show twice.
I traced it down to the accessibleChange custom event found here (lib\templates\url_select.mustache)
if I add $('#id').unbind("click"); before the .on() it fires only once, However, this is not a complete fix. It requires a click outside the select box to fire.