I have the same problem in Ubuntu 16.04.3, but only for certain applications (jabref and texmaker so far).
The comment by @spoolboyy helped: I was using a USB mouse and clicking with the touchpad stopped the drag-and-drop mode.
I am using a Thinkpad X1 Carbon laptop.
I have the same problem in Ubuntu 16.04.3, but only for certain applications (jabref and texmaker so far).
The comment by @spoolboyy helped: I was using a USB mouse and clicking with the touchpad stopped the drag-and-drop mode.
I am using a Thinkpad X1 Carbon laptop.