Collation and sorting for French locales

[barbier at linuxfr dot org (Denis Barbier)]

I was quite surprised to find that sorting for French locales do
not work as described in ISO 14651 and implemented in iso14651_t1.

First let's define an xx_XX locale containing
  LC_COLLATE
  collating-symbol <a>
  collating-symbol <b>
  <a>
  <b>
  
  script <S1>
  
  order_start <S1>;forward;backward;position
  <U001A> IGNORE;IGNORE;<U001A>
  <U0061> <a>;<a>;IGNORE
  <U0062> <a>;<b>;IGNORE
  order_end
  END LC_COLLATE

  $ cat test.xx_XX
  aa
  ab
  ba
  bb
  $ LC_ALL=xx_XX sort test.xx_XX
  aa
  ba
  ab
  bb

Good, that works as expected, the backward directive does its job.
But now, let's add another script definition:
  LC_COLLATE
  collating-symbol <a>
  collating-symbol <b>
  collating-symbol <c>
  collating-symbol <d>
  <a>
  <b>
  <c>
  <d>

  script <S1>
  script <S2>

  order_start <S1>;forward;backward;position
  <U001A> IGNORE;IGNORE;<U001A>
  <U0061> <a>;<a>;IGNORE
  <U0062> <a>;<b>;IGNORE
  order_start <S2>;forward;forward;position
  <U0063> <c>;<c>;IGNORE
  <U0064> <c>;<d>;IGNORE
  order_end
  END LC_COLLATE

  $ LC_ALL=xx_XX sort test.xx_XX
  aa
  ab
  ba
  bb

Now it does not work any more.  If I define <S3> script and add
  order_start <S3>;forward;backward;position
after <S2>, it works again.  Thus it seems that the last order_start
rule wins.  I tried to add
  reorder-sections-after <S2>
  <S1>
  reorder-sections-end
at the end of LC_COLLATE definitions, but this does not change anything.
So how can we make sorting work as expected for French locales?

Denis