This ain´t going to be pretty.
Welcome to world of pc/linux. Everything seems bit off and you need hammer occasionally. All apps that have features more than ten seem to work almost 95% of time as you want them to behave Good thing thou is that xterm and shell works exactly by your command. Nahh...just some apps have weird behaviour.

There is free alternatives but I have to admit that even thought they are nice on some sides they still look a bit "Daddy look what i made" stuff and probably are not as power efficient as default media player.

And to your problem. I would like to ask that what exactly you are trying to do with album art? For me it has worked quite nicely when i have used folder.jpg & cover.jpg in same directory as album. I have never used tags for cover images. Is it even standardised? I would not be surprised if 5 mpix picture as cover image fcks up system whenever it´s full moon. Low resolution images in album folders would be IMO safe bet. Although i do not know what is the correct file name or does it even matter.