I have discovered this same issue. I know tags are specific to a space, so it makes sense that a tag from a sub-space would not return any results if you click it in the parent space tag cloud. My question for the Jive developers is why allow the editing of the tag cloud to include tags from sub-spaces when clicking those tags does not retrieve any results? It seems like useless functionality. The funtionality does work from the root level space, but not for any of the sub-spaces or sub-sub-spaces from that. Please reply whether this is a bug or intentional. Thanks!
Did this ever get answered?