Moving QDockWidget fails, but only on some monitors

I am getting an odd behavior with QDockWidget in Qt 5.7 . I've created a minimal widgets project, essentially all default settings, thrown together by Qt Creator with a main window and two QDockWidgets attached to it. Attempting to move a QDockWidget from one dock area to another succeeds if the window is on my right two monitors, but fails on the left two.

I've recorded a video.
https://www.youtube.com/watch?v=3_VP3rN33HA

Compiling with msvc2013 on Windows 7 64-bit. This does not occur if I build the same project with Qt 5.6 . I'm going to have a coworker try it with his machine, similar environment but I think he's on msvc2015; and also I haven't tried it on Linux yet so when I get a chance I'll build there and see if it gets the same results. I have an OS X build/test environment, but it only has one monitor.

I've been trying to debug this as well as I can without building Qt from source (which would be a major investment of time), but so far I'm stumped. If I break on an event filter catching a mouse release on the dock widget, the QMainWindowLayout::pluggingWidget is already set to null, and I can't find any other events that fire at the right time. I'd like to have some idea of what conditions with my monitors cause this bug to occur before I submit a bug report since right now I've all I've got is "well it's my machine and maybe others too but I don't know".

EDIT: The widgets behave as expected on Linux and on my coworker's computer, however in both instances there were only two monitors, whereas the failure happens on an environment with four.