The change from T113797 (c65b032da5bda2c59059d12494934533320ff1dd) seems to have introduced a bug in sequence expansion, where the input that triggers the sequence isn't always removed from the DOM. It is, however, removed from the model.
The list item sequence exhibits this. (New-paragraph, enter * , see that we get • * instead of just • .)
It's not universal; the link sequence doesn't do this.