Why did this work for me? (iPhone 3GS 4.2.1 JB/Unlock)

[reVain]

I recently acquired an iPhone 3GS after repairing a customer's other iPhone, and he gave it to me as a gift (very generous guy, but it wouldn't charge. I had to replace the charging port to get it to work). After I got the part and repaired it myself, I went ahead and did the redsn0w tethered jailbreak and unlock with the iPad baseband 06.15.00 and then did the greenpoison untethered jailbreak to finalize it.

All was ok until I randomly has Cydia crash while updating iFile, and it literally made my Cydia no longer work and all the associated apps from Cydia to no longer work as well, and made my wifi no longer connect (it would read the WiFi connection, but I could not go online). Read up online and only found the "delete your temp files in your iPhone using OpenSSH" trick, used iPhoneBrowser for the same cause and that didn't work, and just made it worse. I knew I couldn't do a regular restore to get it to work properly, and since I fixed a 1015 error code in the past from another person's iPhone 4 in the past (that's when I learned about it, and fixed it with a simple push click from iReb, even though it was a tethered 4.2.1 jailbreak), I knew I could brick the phone and then use iREB to downgrade it and restore.

I did the iTunes restore and bricked the phone, and then used iREB and it wouldn't work and it stayed in boot cycles. I then decided to try to downgrade to 4.1 firmware, and got the 1015 error code as expected, but then tried iREB again after doing that, and it restored just fine as I wanted it to. And it is now on a untethered 4.1 jailbreak/unlock, and everything works fine again.

So my question is why did that work? Why did I have to hit an error code by attempting a 4.1 downgrade allow iREB to restore my device properly?

[i.Annie]

1015 is a baseband flash failure. But the restore went through fine.