I cannot find any setting to stop this madness, any suggestions?
All the unused using statements are removed when saving, not so great when converting a bunch of projects and manually updating multiple files.
It sounds like you have Code Cleanup configured to run on Save. You can configure this it Tools -> Options -> Text Editor -> Code Cleanup.
Alternatively, you can configure which tasks Code Cleanup performs and set it to not remove the using statements. You can find this under Analyze -> Code Cleanup -> Configure Code Cleanup, or on the lower editor margin in a button with a sparkling broom symbol.