If there are any blocks marked to be infected they will turn to taint even after you disabled it in .cfg,but they won't spread afterwards.So make sure you give it enough time to really stop spreading before you declare yourself crazy.
Check your .cfg for "aura.Taintspawn" some people say you need to disable this but to me it looks like it is only a different name used for same setting,probably from older version.
Bodies of water (rivers,lakes,sea...) can't become tainted,but the taint as the infection can spread through them ; meaning,if you have 2 islands where only one of them is tainted,after enough time both of them will end up tainted.The taint will grow as it usually does through the water blocks,you just can't see it until it emerges on the surface somewhere else.In shallow waters sometimes you can see it spread on the seabed.
Even if you manage to completely stop the spreading of taint you can still infect the land by yourself using vials with taint,magic cauldron...or any similar pollutants.
If Tainted Creeper explodes outside tainted area,it will make even large crater and will also corrupt some blocks.
Tainted Testificates release gas that can make some tainted areas grow even more.
Tainted Sheep can vomit taint.