The tag change updates the last executed changeset in your history table. That beeing said it's a bad idea to tag from outside (as it appears in your case, cause I can't see any tag change in your changeSets).
My advice would be to add a explicit changeSet with only a tag change, so you can make sure the tag is exactly on this entry in the history table. While that does not help you in the case if you are adding more changeSets before that one (then rollback will still be broken), but that seems to be a design decision of liquibase (not to complain about changeSets out of order).