Wrong cover art displayed if either Album tag OR Artist tag are missing
As reported in this thread: http://forum.videolan.org/viewtopic.php?f=2&t=79717&start=20#p306636
There is a bug in VLC with embedded cover art when there is no Album tag set.
In this case, the first tagged file with no Album tag set being opened in VLC will create a sub folder "/art/arturl/254ee9553243878e0f06dfea051798eb" and will drop there the cover art. Then, any and every other tagged file which has no Album tag set will use this cover art without renewing / refreshing the content of this sub folder nor creating a new sub folder.
However some files with a malformed Album tag as seen in this thread http://forum.videolan.org/viewtopic.php?f=14&t=93740&p=310267#p310267 won't use this cached arturl cover for some reason.