Re: MELE PC game won’t stop running.
An additional detail: You don't need to run any of the games for this issue to occur; just starting then exiting the launcher is enough to reproduce the "still running" issue. And yes, I did verify that nothing related to MELE was showing as running in the Task Manager, aside from the OriginWebHelperService, yet Steam still showed MELE as still running.
All of that said, I did figure out the cause of this issue: Origin.
I already had Origin installed on my machine before installing the Steam version of MELE, and apparently it doesn't like that arrangement. Uninstalling Origin, then running MELE from Steam and letting it reinstall Origin, completely resolved the issue.