Decided it was about time I looked at interactive grids. So I logged into apex.oracle.com and added a new interactive grid page to an existing application.
I was obviously previously using "legacy component view" which it turns out will show me the Region Definition but not the Region Attributes (something flashes up on the screen but disappears leaving .just Region Name and the Cancel + Apply Changes buttons.
So I switched to Page Designer view which doesn't seem to do anything useful. I can add new components by right clicking on LHS pane ( very useful if you want everything called "New" ) but clicking on the links under Page Rendering doesn't open anything to edit existing components.
Tried this on 2 different PCs using both IE and Chrome with exactly the same results.