When using the transfer app on Mac OS, it is much too easy too press command-q which will close the Transfer window but also it QUITS Dropbox.
There should be a warning informing the user that they are about to quit the entire dropbox app/engine and offer instead to "close" the transfer window and/or hide it.
There needs to be an intermediary step in this regard.
The app "UA Connect" from Universal Audio does exactly this with their app that is present on the Mac OS menu bar [just like dropbox]. If you press command-q , UA Connect warns you what the consequences of that will be as opposed to hiding it and allowing it to continue working in the background.