And another thing ... I typed in the correct sentence (I wrote it down when it gave me the "corrected" version) and it passed me. Yet it gave me this sentence a third time, as if I hadn't passed. So a double fix is required here..
No, it's supposed to do that. If you get something wrong once, even if you get it correct on the second chance, it often will test you again a third time, to ensure you've learned it. It's reinforcing the material.