I actually used to have this problem as well. Want to know how I fixed it? Stopped using FLAC files altogether. Why? Well on an 8gb device, you can hardly fit any albums ripped in FLAC on it in the first place. But really, why is FLAC necessary? I converted all my FLAC files to 320kbps MP3’s, and in all seriousness, you cannot tell the difference. Anybody who says they can is 1) hearing what they want to hear, or 2) using $1000 IEM’s or monitor headphones.
Not trying to be a pest. I just got tired of dealing with the problems with FLAC, and the album art not showing up. I no longer have any problems.