This is actually a common phenomenon, typically connected with meaning changing over time. Two examples that spring immediately to my mind are:

• Cleave: to cleave to something means to stick tight (this is now an uncommon usage), while to cleave something is to cut it in sunder.

• Let: now means “permit” but used to mean “hinder”. The older sense is broadly obsolete, but is still used in tennis (“let” meaning there was some hindrance to the serve, typically but not exclusively from the ball striking the net).

I suspect “couldn’t care less” being corrupted to “could care less” (which should mean something quite dissimilar) is a related sort of case, but I’m no linguist. I can imagine that all of these cases could be at least partly due to carelessness or misunderstanding of the word or idiom; but again, I’m no linguist.