It seems that DL does not accept straightforward typos when the mistyped word happens to be a proper word. Probably it is not language specific though I cannot tell for sure. I think it would ease a lot of pain is this was adjusted in the main typo detection algorithm.
the people who contribute to the language course, insert those typos, or add them, because many fast typers sometimes get a little typo ;) they get them from reports, depending on the difficulty on the language (by that i mean, the lettering), it may take more time to insert those typos to be valid.
the point is basically to know how to spell it write, but i do agree with the typo issue. but it will take some time to add it,