Just a heads up if anyone else uses VirtualBox and manages to get Seamless Mode stuck on. I was able to find a solution. Shut down all your virtual machines, if they're running, and quit VirtualBox. Open the ~/Library/VirtualBox/Machines folder. Find the folder with the VM that's stuck in Seamless Mode. Open this one. In here, you'll see a few folders along with a configuration XML file. Open the XML file. Edit the line that contains Seamless - it'll say "True", change that to "False". Save and close the XML file. Restart VirtualBox.