By my recollection TinyMCE on it's own doesn't do uploading - it's pure client-side code so is incapable of doing so. Are you talking about an official or 3rd party extension or plugin that has a server-side component?
I think it's the official file manager extension that's doing it - though with the old version that I have, the file manager came built in instead of as an optional (paid, now) extension.