To be honest, after successfully applying what you said, I’m not sure if I worry more about the facts stated in my post or about the solution described in yours
The situation is that it is possible to add an explicit single barline that is visually indistinguishable from a default barline. The latter comes from the most recent time sig; the former makes its own, new, invisible, matching time sig, and you can’t remove it by deleting the signpost. There was more discussion about this last August.