I don't think this has to do anything with the blocking. The blocking system relies on filesystems with multiple streams, and happens on Windows shell (not even kernel) level. So it is simply a kchmviewer problem, and/or the CHM uses non standard html. (a CHM is basically archived html)
Note that kchmviewer can iirc switch viewer. khtmlviewer vs webkit or so. Try to switch viewer and see if that improves matters.