So maybe this is platform dependent. Either way this is certainly a bug. Factorio should refuse to open when a second instance is launched at least. Can this be moved from "Not a bug"?

This is definitely a bug, to allow the user to possibly silently lose their game? Starting a new instance of factorio in the same directory should show an error message and not start at least!

If you are playing a game of factorio and you open another instance of factorio, the first game cannot be saved because the second instance deletes the temp folder.

To reproduce:

Open instance A of factorio
Open a game (campaign or free play) (this creates temp and temp/currently-playing ...

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My post falls on your 'untempered vitriol' category.

Why would I try to install something made in a framework, whose developer doesn't even try to cater to the platform I use? Surely I'm not expected to install a 3rd party framework implementation that may or may not be able to run the stuff ...