At first I wasn't sure which blog to post it to. Then I realized it's not necessarily a test mode so I decided to post it to the main blog. I discovered this in Visual Boy Advance. From the description:
This is a memory hack for Sonic Advance. Open a Sonic Advance ROM in Visual Boy Advance and then go to Tools and Memory Editor. Go to 00000214 and change it from 0002 to 00FF. Then click on the emulator window and it will be black. Go back to the memory editor and change it back to 0002. Click on the emulator window and it might say something like "Unsupported ARM mode 18" and then this will happen when you click OK.
EDIT: I have decided to host the savestate of the gray boxes glitch and link to the rom:
- Get the savestate from: http://www.mediafire.com/upload_complete.php?id=oyomg5zwzqm
- Get the ROM from: http://www.emuv2.com/index.php?page=rom_dl&rid=1575
- Due to legal reasons, I cannot give you a MediaFire link for it.