This appears to be a bug in version 3.3.1 of the Airdroid desktop app for Mac. Each time I quit by pressing Command-Q, the Mac (1) unpairs with my wireless mouse and (2) inserts a letter "q" in whatever application becomes foremost after Airdroid has quit. Supposing I had a whole paragraph selected in a text editor just behind Airdroid, that paragraph will be erased and replaced with "q". Regarding the mouse, it's a Logitech mouse connected through the Logitech Control Center. In Mac OS System Preferences I have to open the LCC preference pane in order to unpair and re-pair the mouse whenever this occurs.