Pixel precise. Of course. I could kick myself. I suspected it might be because the node was somehow of an indeterminate size. It worked, of course. Thanks MM. Respect
As to why I'm doing it that way, two main reasons.
First, there's a lot going on in this scene. Rather than set up nodes for everything, I've found in the past that can make the scene run slowly in the interpreter, and I don't want to take that chance in the compiled version. So I try to minimise the number of nodes and poke and pop them with what I need them to contain, because it's faster in execution.
Second, I simply did not realise I could use a Region entity to contain sprites, but only because SceneEdit won't allow it.
BTW, the debugger simply didn't tell me what I needed to know. It doesn't give the node cursor state, doesn't mention the width of the node, gives the 'filename' as null even though there's a .png in it, and although I'd done several things to my multidimensional global 'WallPuzzle', it wasn't even mentioned. Is there a document anywhere on the deft and skilful use of Debug?
Cheers