Description of problem:

After "du ", completions of paths with special characters in them should be escaped or quoted, but they're not.

Try creating a directory called "dir with spaces". If you type

  cd dir

and hit tab, it'll complete as

  cd dir\ with\ spaces

which is correct. But with

  du dir

it'll complete as

  du dir with spaces

which goes wrong because it's treated as three separate parameters.