Drag and Drop of Issues in Milestone view not working correctly

I've just updated to GitLab 8.5.0

It's not possible to drop issues to an empty list.

Steps to reproduce:

1. create new milestone
2. create 1 new issue for this milestone
3. go to milestone view (where you can drag and drop issues: unstarted, ongoing, completed)

Now you are able to drag the issue, but you can't drop it anywhere.

This does not happen, if you try to drop an issue within a list that contains at least 1 issue.