I've been using the Bépo keyboard layout for years in Ubuntu, labelled as "French (Bepo, ergonomic, Dvorak way)".
Since upgrading from Ubuntu 17.04 to 17.10 (Artful Aardvark), I now have to use Ctrl+Shift+V to paste, instead of Ctrl+V. This is unintuitive and I'd like to change it back, but I'm not sure how to revise it. In the system settings, there are keyboard shortcuts for starting the terminal etc, but nothing about sabotaging the effect of buttons such as Ctrl. There are no shortcuts listed for copying or pasting.
I suspect that Ubuntu itself has used a faulty key file, as I recall having a similar problem with Windows a while ago, having to mess around with Microsoft's Keyboard Layout Creator.