BUG #8399: inconsistent input of multidimensional arrays

The following bug has been logged on the website:

Bug reference: 8399
Logged by: Alexey Borzov
Email address: borz_off(at)cs(dot)msu(dot)su
PostgreSQL version: 9.3rc1
Operating system: irrelevant
Description:

PostgreSQL documentation states:

"Multidimensional arrays must have matching extents for each dimension. A
mismatch causes an error..."

This is not completely true:
postgres=# select cast('{{1,2}, {3}}' as integer[]);
ERROR: multidimensional arrays must have array expressions with matching
dimensions
LINE 1: select cast('{{1,2}, {3}}' as integer[]);
^
postgres=# select cast('{{1}, {2,3}}' as integer[]);
int4
------------------
{{1,NULL},{2,3}}
(1 row)

Trying to use an array constructor yields an expected error in both cases.

Confirmed on 9.3rc1 and 9.0.13