Shortcode update creating copies of itself

I updated the shortcode plugin after the most recent update and it immediately threw an error - I found clones of all the files in the plugin folder, all called 'xxx 2.php' where 'xxx' is the file name. I assumed the update had gone wrong and threw out all the doubled files (which included non PHP files - js, readme.md, map, etc).

Reloaded and it has worked for five minutes before throwing the same error again, so I'm assuming it's generating these files itself.