When playing as a sessile organism in a single patch, like in a short run I just did, you may find yourself in the center of a cluster of mitosed cells, if you don’t move. The cells build up over many generations. They will automatically progress closer to your current evolution stage if left too long, but they’re usually 1-2 generations behind you.
These cells count as part of your species. You can’t attack them and they won’t attack you. Using the binding agent on them works, even if they don’t have one of their own. As a result, you can form a cell cluster, possibly 16 cells in number, with only two of them having binding agents. This is a relatively minor bug, I suppose, and not super important.
Cells are marked as members of a species when they spawn. This is going to be kept as this prevents stuff like your “old” species immediately killing you after you exit the editor or become multicellular. There’s been a ton of bug reports about your old species killing you instantly when you become multicellular, so old members of a species being still considered the same species is very minor problem compared to that.