A subrepo pull or subrepo clone commit saves the SHA of the parent commit into the .gitrepo:subrepo.parent config. If this parent is later on changed due to a rebase, subrepo.parent becomes invalid, which breaks tracking. I suspect the main command that breaks is subrepo branch.
Could this be fixed by getting the parent through rev-parse or some other method that works well with rebases? Or is this a limitation of the tool?