I was working on a space plan on a project today & came across something slightly annoying.
I created a group for each workstation with it's associated chair. Copied it all over a plan. Then copied the group to the plan above. After doing this for 4 full floors, I then realized that I needed to have room separation lines to create rooms so I could easily color code the plan. So thinking that since I already have the groups I can just add room separation lines to the group & voila I'd be done in 5 minutes flat. Everything was fine until I started editing groups that had been copied to the floors above. All of a sudden after editing a group on floor 1, "random" room separation boxes showed up on floor 1. After some investigation, I discovered that these were actually from rooms on floor 2. Some of the instances of the group their room separation lines were located on the floor 1 even though the group was located on floor 2.
I tried copying & pasting the lines in edit group mode from floor 1 to floor 2 to try & fix the problem but that only made things worse. The groups that were on floor 1 now had their lines on another level. The only solution that I found to work was to delete & replace the offending groups (which is a pain). So instead I created new groups of just room separation lines and spent more time copying those around the plan.
So as a warning: Room separation lines & groups do not always get along.