Technically this isn't a bug per se. It primarily arises because of the various encodings of text files, this is not something that will ever go away and is well beyond Microsofts ability to resolve. There are several main standards used for encoding in let's call it 'western' countries, though this is an oversimplification and it has more to do with the languages/characters that are being encoded.

ANSI/ASCII are historic character sets for primarily English text (there are many other 6,7 & 8 bit variants), UTF-8 and UTF-16 are Unicode extensions upon this simple set to extend to most known written characters across languages/cultures. However, before the emergence of such Unicode standards each language tended to get it's own code-page/encoding.

All that being said, UTF-8 (without BOM) and ANSI appear exactly the same to a machine if there is no characters used beyond the first 128. So Visual Studio has to make a guess unless you tell it what to expect or systems start adding the BOM to UTF-8 files when they are created. In your case the problem has been created by whatever system created the text file not adding 2bytes at the start of the file (the BOM) saying this is a UTF-8 file.