When the mouse is near an object, it is highlighted to show the element that will be selected when the mouse is clicked. This is an excellent feature for giving the user feedback about the state of the selection that will result from the click action.
If an element is part of a group, only the individual element is highlighted and not the entire group. This makes the indication of the resulting selection state not match the actual outcome. It would also be useful to hover the mouse over elements to determine which are grouped.