This may not be a Thunar problem. This may be due to a recent upgrade to glib2. See here, particularly comment #12:
I am running Manjaro with the XFCE GUI. My laptop and desktop both have the same version of Manjaro, same 4.1 kernel, and the same version of Thunar, yet the laptop isn't having the problem.
I just checked and my laptop version of glib2 is glib2-2.44.1-1- the one the commenter said is stable. Yes, he's talking about drag and drop- but the fact that my laptop with the earlier version of glib2 doesn't exhibit the problem can't be a coincidence.
I don't have my desktop computer on right now- the one that IS having the problem- but I'll bet that when I turn it on tomorrow and check- my version of glib2 will be the newer problematic one, glib2-2.46.0-2.