I have found a bug that is related to the movie title & year not been updated in the movielist and have fixed it for the next release. It will be uploaded within the next couple of hours.
The fanart disapearing is not related to MC. Check the filenames of the fanart, it is possible that there is a naming bug somewhere, but MC does nothing that would delete it.
To ensure scraper accuracy the use the year in the file/folder name, eg.
Spider-Man II (2004)
Die Hard II 
This will do a search on IMDB for "Spider-Man II" and MC will look for top matches with the matching year, the vast majority of movie searches will return correct using this method, including those 2 movies.