Grouping selected shapes/objects

[elvintoh82]

Say for example i have a unit of jenga block, but it is occluded by a ruler over it (and hence splitting my jenga block into 2 parts).
When I use the autolabel and click one part of the jenga, it is smart enough to highlight (draw the polygon) on the 2 separate parts of the same jenga. The issue is, it is recognised as 2 objects, hence saving 2 separate jengas.

I would like these 2 parts to be recognised as 1 object (consisting of 2 shapes), and thats when I found the "view->group selected shapes" functionality. I managed to group the 2 parts together, and a dashed rectangle was drawn on them, but the dashed rectangle grouping keeps disappearing when I switch back and forth between images, as if they have never been grouped before.

Could someone advise if this is a bug of the grouping functionality? Or have I misinterpreted how the grouping should be used?