After exiting the game Steam insists that it is still running. And only shutting down Steam will resolve this.

I checked the local files but they were fine. I consistently got this result every time. 

When starting the game afterwards the error code was 740.

Recently the bug has not happened again. 

Hmm that is strange - sometimes it takes a while to sync up all the cloud saves after closing, but I don't think it'd appear as "still running" - will keep an eye out.

This "still running with closed game" problem isn't actually tied up to MewnBase. It's a Steam problem as I had it with other games (Valve's too)

There can be cases where sometimes the Java process isn't getting terminated correctly/completely (which can also cause this issue).  Hopefully I fixed at least the more obvious culprits of that in the latest update, but if it's still happening to anyone in 0.50+, just let me know :)