interesting to read this

I have a similar situation but I can control it really
I bought this sort of blue sedum, that is quite lovely, several years ago
Took a couple of cuttings from it and planted them. Thy took readily
Continued to do this that first year.
NExt year had several plants and year after that more than I needed
Began giving them away.
Noticed that somehow tiny plants would grow up every where including in the interlocking patio and driveway.
Don't know where the little seeds or whatever ever came from

I have made a solid area of them in a place in the garden, under a large tree that was not able to grow anything. And they stay small and short and look rather nice
Yet little seedlings pop up in odd places
I just keep pulling them out when tiny and have control enough of it

But is I thought unusual in Sedums.