I iTunes had a very similar "autocomplete tries to be helpful but causes chaos" bug a few years back. If you clicked to edit the artist column it would autocomplete from the list of other artists in your library. However, if your desired artist name was shorter than one it's trying to autocomplete, it would forcibly append the rest of the name from the longer artist.

e.g. if you typed "Ross" and wanted it to just be "Ross", but you have any track by "Ross from Friends" in your library, it would always append " from Friends" no matter how many times you tried deleting it.