Do you have an idea?

I notice how frequently I keep making some silly spelling mistakes when I write. Though I know and understand those and have been told about this but some how when I am writing in my flow I repeat the same mistake again? I might have written at least 100 times THERE instead of THEIR in my blogs. And it never strikes me when I write. I have written Dissappoint instead of disappoint. There are many such errors which if I have to write again am going to do. Similar mistakes we do in our day to day activity. It seems that the brain works in a set manner.

Does any one have an idea what this disease(i am not sure if this is a disease) is called? What could be the way to get out of this?