In the first instance I did it on the Client group management page, as that was the page you had reported 
I have now added it to the other pages!
No, sorry. I've broken something... sigh. I'll come back to you once it's done
I think we managed to get it into a "best of both worlds" situation yesterday, it keeps the canvas of the table scrollable, which is needed sometimes horizontally, and also allows the drop down to render outside of the bounds of that container.
I'm no JS professional, but it seems to do the trick! Please check - and remember to clear your browser cache before trying.
Working fine now. Thanks.