Group to shape

[CaptainCrunch]

Having a problem understanding how Group to Shape works.

I made 6 points: Imagine the four vertices of a rectangle, then two more points say 5 units higher than the top two of the rectangle. I group to shape the 4 points of the "bottom" rectangle. Then when trying to group to shape the uppermost 4 points to make another rectangle on top of my first one, it does so, but my original rectangle disappears.

Many thanks if you can let me know what I'm doing wrong.