If the encryption on your root drive is broken or breakable, it's game over for that kind of system. The scenario 'I'm plugging in random encrypted drives into my system which is itself not encrypted' is not a sane one any OS maker is going to spend time mitigating. Your editor could have left stuff in a backup. The file contents might be sitting in swap. You copied the file over and forgot to delete it. Or you deleted it but not securely. Etc, etc, etc.

As I said, I can't think of a non-contrived scenario in which this is an issue and to me, the one you're describing is strictly in the contrived category.