Woops! Looks like you've found a bug, plain n' simple. My editor logic is incorrect when you only have a single object selected. (You'll see it work correctly if you have two or more AnchorableBehaviours selected.)
Good news is I've fixed the issue and it will be resolved in the next release of the Interaction Engine. Less good news is, of course, that you don't get the fix right now. Well, you actually can:
Modify your AnchorableBehaviourEditor.cs (found in
Here's the relevant commit, with a diff for the file so you know what lines to change.