Also, another weird behavior I noticed: When I look up for example the language string r__fields_manage (this exists twice, but I am talking about the outdated one tied to the Downloads app, as there is no English text provided anymore), it still holds my translation. When I delete my translation text and save the change, then leave the language section in the AdminCP, and go back there later, the language string again holds my translation. So deleting and saving does not seem to empty it.
The same goes for a couple more language strings. Their text cannot be deleted/emptied as it always returns once I reopen the translation.