Randsequence & interleaving productions

Folks,
The explanation of interleaving option for randsequence in LRM is unclear to me.

The is the description from LRM:

The rand join production control is used to randomly interleave two or more production sequences while maintaining the relative order of each sequence.

Here is an example from LRM:

randsequence( TOP )
TOP : rand join S1 S2 ;
S1 : A B ;
S2 : C D ;
endsequence

The following is the output for the above example:

A B C D
A C B D
A C D B
C D A B
C A B D
C A D B

If rand join randomly interleaves two productions then I would expect two combination for the above: a) S1 S2 b) S2 S1).

If this is true then the sequence for a) A B C D b) C D A B
But there are at least 6 sequences as per LRM.

Need clarification …

In reply to shatrish:
There is no interleaving in the sequences you expected. The interleaving occurs between the productions within S1 and S2.