Hi Phillip, this seems as an issue/misunderstanding about where a new container appears.
Basically, the grey lines indicate nested stacked containers, and they try to indicate that with the label: `S[S[S[x y z]]]` indicates that that line belong to a stacked container that holds *single* child container `S[S[x y z]]` (note one less `S[]`). The last grey line (`S[x y z]`) is the actual stacked container that holds all your stuff (`x y z`).
You should be able to get rid of these by focusing the inner-most stacking container and try to move it around; that usually works for me.
I do not have a sufficient understanding of the container tree manipulation to advice any further, but maybe the i3 docs on this topic [1] could shed some further light on it.
[1]: https://i3wm.org/docs/userguide.html#_tree
Hope this helps! -- Jan Staněk Software Engineer, Red Hat jstanek@redhat.com irc: jstanek