In Windows, I suddenly see a black-bordered transparent rectangle, instead of the full contents of the window, when I drag it. I probably hit some magic key (wonder which one) that turned full-window dragging off, but how do I turn it on again?
Note: the question mentioned by David is not a duplicate, as this behavior occurred without me explicitly changing the setting, and after a few hours of doing nothing, it magically restored itself.
Cisco Webex turns off a function in Windows that allows for transparent windows and and taskbar (In Vista it was called Aero, I'm not sure if that's still the case in Windows 7 and 10).
The reason it does this is because the software is designed to let people see your screen if necessary. When you are sending your screen to someone else the graphics card doesn't get a chance to process the output as it's being sent through the network as well. Although it's possible for a computer to capture the output of the video card, it can be extremely slow. To cover most use case scenarios, Webex just turns transparency off.
