All of the property assignments to PUA characters (except the GC) are purely informative. The property assignments that are there are simply based on the likelyhood of property assignment, and can be freely overridden by implementations. It is just more likely that PUA characters are bc:L than that they are bc:ON or bc:R.
Similarly, there are no numeric values for any of the PUA characters: that doesn't prevent anyone from assigning PUA characters to numbers and giving them numeric values (and types). Nor is someone prevented from given them Word_Break properties, etc. While this is stated in the standard, we should probably also note it in the UCD annex: http://www.unicode.org/reports/tr44/. Mark
