I came across an issue where I got unexpected behavior, but I can understand the logic with what it is currently doing.

As a minimal example, here is a setup to reproduce the issue. I have placed 2 red bricks, 2 green bricks, and 2 blue bricks in the workspace. I group the 2 red bricks together (call the group "Red"), the 2 green bricks ("Green"), and the 2 blue bricks ("Blue"). I then group the Red and Green groups together, and call it "Christmas".

Now, I click on the "Christmas" group in the Groups box to select that group (the "Red" and "Green" bricks), then choose Invert from the selection tools menu. The result is that all 6 bricks are now selected, instead of just the blue bricks. This seems to be because when the "Christmas" group is selected, the "Red" and "Green" subgroups are not selected, and so when inverting, it selects "Red" and "Green" as well as "Blue".