The only workaround that I have found, that does allow one to drag & drop, is to have a third column, the File Browser, open. Find where the files are that you want to work with, and that column allows one to drag & drop.
I find it tedious, plus it has taken me out of my "comfort zone," whenever I used Picard prior to this update. But, you will not find me screaming for a "fix," it's not that serious.
But anyway, that is my workaround using Mac OSX 10.11.6, so I hope it works/has worked for others using a Mac.