Minor usability irritation: Rancor complains about "Invalid tag number" on a completely empty line. You tend to automatically press enter at the end of a field, meaning you may have an empty line at the end of the record... and then Rancor complains when trying to save. Should instead just silently discard the empty line at the end before saving. Same complaint happens if there's an empty line in the middle, but I'm not sure if that should be silently discarded.
Can't remember when this was fixed, but now blank lines are all stripped.