Currently, locale translations and configuration translation strings are kept in sync for not to overwrite each other's changes. Locale is used to translate configuration strings when they have their default value but not anymore when they are updated.
When you change a configuration string in the source language, the translations for that string still keep updating the locale translations for that
Steps to reproduce:
1. Standard install with English language (default) and Spanish language. All translation modules enabled. Spanish translations imported, etc..
2. Check there's a translation in locale for the string "Tags" (Spanish: "Etiquetas") or create it otherwise.
3. Configuration translation for the Vocabulary "Tags" should have the same string (they are kept in sync).
3. Edit the original vocabulary, Tags, rename it to something different, like "Colors".
4. Translate the vocabulary name, (Spanish: "Colores").
5. Check the locale Spanish translation for "Tags", in 'User interface translation' is now the new string: "Colores". This is adding a wrong translation for a localization string (The same string may be used for other purposes in the site).
Once you edit the original source string in the configuration, the translations for this new string should not update anymore the original locale translation for the old source string. These are different strings now.
Since po files may be shared accross sites, having wrong translations in them will get also wrong translations for other sites where the same po is imported.