OK, so this is something that has bugged me for about a decade now. In all three DKL games, the sprites blur occasionally when there's any kind of lag, at least when I play it on any of my handhelds. That is, at times, random pixels disappear or are in the wrong spots. It seems to be especially bad in DKL and seems to be not as bad in DKL3 as the others. And obviously, my cartridges aren't defective, or else it wouldn't happen to all three cartridges that I have O_o
Since I started using emulators in 2007, and played the DKL games on it, one of the first things I noticed was the lack of this sprite blur. I was surprised (in a good way) to see this happen; it made the game feel a lot "cleaner". This led me to play the games on VBA more than on the real handheld itself. And whenever I went back to my real GBA SP (which is what I play the games on, although the sprite blurring appears on a GBC and GBA also), it was difficult due to the distracting blur, which at that point I was no longer used to.
Now, I got a Super Game Boy a couple of days ago, and noticed the same thing as I did on VBA: The sprites didn't blur! Again, this surprised me, since the same cartridges that have the problem on all my handhelds don't have the problem on SGB. So now I know that the sprite blurring seems to be some hardware issue, as opposed to sloppy programming.
I don't have a brick Game Boy or a Game Boy Pocket, so the only thing I have left to wonder is: Do the sprites blur at all on either of those two systems? If not, then the GBC and GBA aren't perfectly backwards compatible with the original GB, as they have the sprite blurring problem. If they do blur, then Rareware didn't bother to test any of these games on the handheld, and only really optimized it for SGB. Either way, I'm curious, and it's weird how the games perform differently on different systems, even though they're supposed to all be compatible with each other.