1) This is a bug and may happen on Windows 10. I’m working to fix it in the next release of Mosaico. In the meantime you may try to close and re-open Mosaico as a workaround.
2) This is due to how Mosaico tries to understand when a window is moving to trigger its overlay mode. Not all apps behave the same, so it may happen that the overlay is triggered at the wrong moment. Thank you for reporting this with Quicken, I will investigate on it and fix this problem asap.