"Show Referring Objects" greyed out

I have a simple test ActionScript AIR app. I wanted to check out the show referring objects feature, so I set a breakpoint but when I right click on any object in the variables window, the "Show Referring Objects" option is greyed out. Does this need to be enabled somewhere or does it depend on something I haven't done? Or is it not available for AS3? I'm able to debug fine, but this one feature just doesn't want to work for me. Thanks.