Looking at the code I dont see any difference in the behavior whether a picture is matched the first time or after you adjust the title and a picture is then matched. In both cases a single user picture is saved - thats the point of this tool is to download pictures and save them to the user pictures folder and perhaps you saw the tool as doing something different.
For your first point, I expect what happened was you already had a picture in your pictures folder and when the artwork download tool is opened, MB checks for existing pictures and unticks an item if it already has a picture. Only the user pictures folder is checked, not the cache.
The next time you run the downloader and have the same files, the status would say "Image already downloaded". So I dont see any bugs.