There isn't currently a way to change an adopted forums category, an adopted forum always keeps its own category (the one it's been given on the home board)
I tried moving one above Random Topics so I could see which was which, but it stayed where it was!!!
If you ever see changes you made that don't seem to have taken effect try doing a hard refresh on your browser; hold down Control + Shift + click Refresh on your browser or hit F5 to get a current copy of the page you're veiwing. Some browsers won't actually reload the page you made changes to and doing the hard refresh allows it to get the newest copy off our servers.