Oh gosh. I think we'll need to see an example of this problem.
When I select multiple objects, and click any one of the a 2nd time, the rotation center is in the middle of all of them as a group. It's the same as if I had Grouped them. The rotation center should be in the middle of all as if they were grouped.
You must have some other situation happening on the canvas, and I would need to see it, to be able to comment on it. Possibly you have some nested groups, or you've entered a group?? Or possibly you have more selected than you thought? Maybe someone else already has an idea what you mean, but I would need to see it in an SVG file.
