Questions regarding U+FD3E ORNATE LEFT PARENTHESIS and U+FD3F ORNATE RIGHT PARENTHESIS

If you compare the properties (from UnicodeData.txt 5.0):
  0028;LEFT PARENTHESIS;Ps;0;ON;;;;;Y;OPENING PARENTHESIS;;;;
  0029;RIGHT PARENTHESIS;Pe;0;ON;;;;;Y;CLOSING PARENTHESIS;;;;
with:
  FD3E;ORNATE LEFT PARENTHESIS;Ps;0;ON;;;;;N;;;;;
  FD3F;ORNATE RIGHT PARENTHESIS;Pe;0;ON;;;;;N;;;;;
you find:
1.) The parens with LEFT in their name have the General Category
    "Ps: Puntuation, opening", as it is appropriate for LTR use as
    with Latin.
    Corresponding, the RIGHT parens have "Pe: Punctuation, closing".
2.) Unlike the "ordinary" parens, the ornate ones have the
    Bidi_mirroring *not* set. Consequently, they also have no
    Bidi_Mirroring_Glyph property defined in BidiMirroring.txt .

Thus, all is OK as long as the ornate parens are used only within
LTR text like Latin.
(In fact, I found ornate parens in a German Hadith comment to denote
translated citations of the Koran.)

But, as the ornate parens are within the Arabic Presentation Forms-A
block (FB50-FDFF), I presume their primary use is for Arabic (i.e.
RTL) text, where a RIGHT paren opens and a LEFT paren closes.

This leads to my questions:
a.) Why U+FD3E has GC property Ps and U+FD3F has Pe, and not vice
    versa?
b.) Why U+FD3E and U+FD3F have the Bidi_mirroring property not set?

- Karl Pentzlin