After hearing that Super Meat Boy is finally available for Linux via Steam I've gone back to playing it and imported my already existing save game into Steam by moving it to the steamapps folder. Now I'm facing the problem that the achievement "The End" is not getting unlocked, although I've beaten Dr. Fetus in the Light World (and every other Light World level except those in Cotton Alley) multiple times (both before importing the save game into Steam and after), which, according to all the information I found, should unlock it.
I've also tried starting Steam and Super Meat Boy on Windows but that didn't help either. Other achievements are getting unlocked without any problems.
Now I'm wondering if there are further requirements for the achievement or if this is (yet another) bug in one of McMillens games? If the latter is the case, is there any workaround like the achievement fix for The Binding of Isaac? If not, what else can I try to get the achievement?