Selecting an object and opening the button dialog adds a layer of grouping to the button. But, if you leave it set to "Do Nothing" the grouping doesn't go away. Selecting the object again and doing the same thing again adds another layer of grouping. Just selecting an object to see if there was a button definition on it adds a layer of grouping, regardless of the other layers that were already there, and regardless of if you assigned any action to it at all (unless "Do Nothing" is an "action").
What you end up with is a bunch of useless, superfluous grouping layers. See attached.
This behavior is the same in 16 and 17, since the inception of the Object Palette. (I guess I just never noticed it before.) I haven't tried it on Windows, but this behavior is consistent on OS X 10.11 and 10.13 (El Cap and High Sierra).
Help me understand the logic of this. Failing that, is there any interest in fixing it?