Normally I have the tab close buttons "turned off" when I am using MC, and just close the tabs via middle clicking on them (not showing the tab close button saves a ton of space in the tab row if you normally have 5+ tabs open). Today however, I was experimenting with the tab close button and I accidentally right clicked on it, which caused MC to shut down.
Playing with it a bit, I noticed a tooltip indicating tab close right-click is supposed to close all other tabs (which is a great idea!). Playing around further, this intended behavior works perfectly as long as the close button is the active tab. If you right-click an inactive tab close button though, MC grinds on it for a few seconds and then shuts down. This behavior is 100% repeatable.
I doubt this is a new issue with MC31. I just never noticed it before since I typically do not have the tab close buttons even displayed.