casting strings to multidimensional arrays yields strange results

Casting strings to multidimensional arrays yields strange results.  In one
case there are discard values and the other a value magically appears.
Trying both of these with the array[] constructor syntax yields the
expected:
ERROR:  multidimensional arrays must have array expressions with matching
dimensions

Tested on both 7.4.3 and 7.5dev.

Kris Jurka

jurka=# SELECT '{{1,2},{2,3},{4}}'::int[][];
     int4
---------------
 {{1},{2},{4}}

jurka=# SELECT '{{1},{2,3},{4,5}}'::int[][];
        int4
---------------------
 {{1,0},{2,3},{4,5}}