Hello,
I had tried it both ways, but it continues to be an issue.
The blue line under the dropboxes indicate where a black line generates when I click on one to drop.
The Twentyfifteen theme (my apologies) is version 1.5.
I’ll shoot you an email to follow up on this. I’ll also post the resolution once it’s been fixed, so that others with this problem can identify to troubleshoot.
Thank you!
E.