VirtualBox on OS X with Windows 10 guest and the ctrl key

Karabiner allows you to disable ctrl+left click on OS X. That will, by default, do the same thing that right-click does with a mouse. You choose the following option to disable it:

So here's where things go bad. If you run VirtualBox and you run a Windows 10 system, you have to turn this off. I believe I had this on due to an early version of VirtualBox not handling ctrl+left click, but they seem to have fixed this in the latest version... ironically my workaround that fixed my issue now breaks it!