The incident reported in https://translatewiki.net/wiki/Thread:Support/FuzzyBot_copy-pasting_English_lines_to_Danish could be avoided if GettextFFS would ignore fuzzy headers (that it uses to determine whether to read msgid instead of msgstr) would be ignored for translation files.
Outcome
We improved Gettext file format parsing code to avoid situations where source language strings would incorrectly be imported as translations.