Probably the caching issue.
Images placed in the root of ./indexArtwork will match to any item in the browsing hierarchy (any value from any index). If you have an artist and producer with the same name you can place the images in separate folders and MinimServer will use the appropriate one e.g.
Code:
./indexArtwork/Artist/name.jpg
./indexArtwork/Producer/name.jpg
The folder name should reflect the tag being used.
MinimServer will pick the best match, so you could leave artist images in the root and put producer images in ./indexArtwork/Producer.