AMAZING!! but...

This game is very good. I have played and replayed it many times. But the reason Im irritated is because in this game. If you beat the game with sonic. You unlock tails. Then play the game with tails and you unlock "sonic and tails" but... I have beaten sonic 1 with every character and I have earned all the Chaos Emeralds with every character. But for some reason it isnt unlocking knuckles! I go to the character select and his picture is black. And yes technically I have 18 Emeralds. Please fix this glitch so I can unlock knuckles! I have unlocked him in previous playthroughs. But now I fear I may have to replay sonic 1 with "sonic and tails" and I will if I must but I rather wouldnt

Mr A man about Sonic The Hedgehog Classic, v2.1.2