The morphology of typing errors?

The title of the last post on this blog now reads "Sentence structure mistakes" but until a little while ago, it was "Sentences structures mistakes". That's a pretty striking case of something I see very often, in emails and in letters going back to the 19th c.: -s suffixes wandering or spreading around on words where they don't belong. This seems far more common than similar speech errors, though that's a mere hunch with not a speck of support. Is there work out there on this that I just don't know about?