I noticed an issue when rotating blocks with the shaded viewport option enabled.
The first reference point is always selected correctly, but the second point does not allow snapping when the viewport is shaded. If the display mode is switched to wireframe, the second rotation point is selected correctly.
This is an outstanding bug and has long since haunted Rhino. Perhaps McNeel thinks this is standard behavior it happens to me all the time and with standard objects not just with blocks.
RM