BUG #6087: Unnest with multidimensional arrays

The following bug has been logged online:

Bug reference:      6087
Logged by:          Maxim Boguk
Email address:      Maxim.Boguk@gmail.com
PostgreSQL version: 9.0
Operating system:   Linux
Description:        Unnest with multidimensional arrays
Details:

I not sure is it actual bug or intended behaviour.
In documentation unnest described as:
"expand an array to a set of rows".

However in case of multidimensional arrays documentation is misleading or
actual behaviour is wrong.

Test case:

postgres=# select unnest(array[[1,2], [3,4], [5,6]]);
 unnest
--------
      1
      2
      3
      4
      5
      6
(6 rows)

I think correct result must be:
unnest
------------
{1,2}
{3,4}
{5,6}