How about the following proposal (from Michele's suggestion):
After a group of objects are selected, we draw the bounding box that we are using. If the mouse cursor is inside the box, it is green-ish, if it is outside the box, it is orange-ish. This can be both a visual indicator of whether the action will affect the selection as well as the selection limits.
The point about object inspector is a good one.
How about the following proposal (from Michele's suggestion):
After a group of objects are selected, we draw the bounding box that we are using. If the mouse cursor is inside the box, it is green-ish, if it is outside the box, it is orange-ish. This can be both a visual indicator of whether the action will affect the selection as well as the selection limits.