There is an annoying bug related to the display modes, more specifically when some object types are excluded from displaying and they are part of a group. For example, if I set a certain display mode to not show point objects, once I switch to that display mode and try to select a group consisting at least one point, window selection will fail to select all the objects inside that group! However, cross selection works in this case. 
Here is a video that shows that strange behaviour.
Hi Bobi - I think you’ll find that is consistent with other contexts where members of a group are hidden - e.g some are on an off layer, etc.
-Pascal
Hi Pascal, unfortunately, this has nothing to do with layers and purposeful “locking” of the objects in the viewport to exclude them from being selected. As I mentioned already, those grouped objects could be still selected, but only with cross selection from right to left direction. This is not possible when locking an object by locking its layer. I’m pretty sure that this is a bug instead, related to the display modes.
On a side note, but maybe related to this topic, I think that selecting a group consisting at least one hidden object must at least display the selection of the hidden object, so that the user could be informed about the possibility (or risk) to modify a hidden object by accident.
In this video example, I created two boxes that I grouped and then selected one of them by Ctrl+Shift. Then I hide it, leaving the other box visible. Once I select the visible box, the Command line says that I selected 2 objects. In my opinion, Rhino much display the (yellow) wireframe of the hidden object that was actively selected, despite the fact that it’s not a visible object. That particular wireframe of the hidden box is actually displayed for a brief moment once I modify the visible box via move, scale, rotate. This is nice, but I would love to be able to see the initial selection of the hidden box as a clear indication that there is some hidden geometry that may be accidentally modified without the knowledge of the user.
The Gumball is also targeted to the center of the visible objects in the group, while in reality there may be some hidden objects (portion of the same group) located far away that will be also secretly affected by the modifications.
