The bug has been fixed and the limitations have been removed. New String::LCSS_XS 1.1 can operate on strings in either internal format (UTF8=0 and UTF8=1), it work with any string (not just those with chars <256), and strings containing byte 00 are now acceptable.

If both strings only contain bytes, you'll get optimal performance by making sure they are downgraded (UTF8=0 format).