ok. I looked into it.... It's an emulation problem. I tried with the SPS IPF's and the config in GBAmiga. I got the crawl crystal and tried to switch. Every once in a while, you end up going invisible.
So, I reloaded, but with everything set to highest compatiblity (cycle exact, 100% sound, OCS, A500, etc.). I got the crystal and it all worked fine. Never once did I go invisible.
So, whether the ADFs you guys are using are screwed or not, I don't know. It's likely that their not.
It shouldn't take very long to test this. It took me 5 to 10 minutes to get the crystal on that level. Go into the first cavern and run through that. You'll pick up 2 keys. Exit the cavern and you'll end up using one of these keys almost immediately at a door to the right. From here, just keep on going up. Eventually, you'll find the crystal.