BUG #8150: NULL emements lost when casting result of unnest()

The following bug has been logged on the website:

Bug reference:      8150
Logged by:          Erwin Brandstetter
Email address:      brandstetter@falter.at
PostgreSQL version: 9.2.4
Operating system:   Multiple
Description:        =


PostgreSQL allows to cast the result of unnest() directly. However, I found
inconsistent results with NULL elements in the array. With some array types
NULL element are lost, while they are retained with others:

SELECT unnest('{4,NULL,1}'::int[])::text;

 i
---
 4
(null)
 1

SELECT unnest('{1,NULL,4}'::int[])::int8;

 i
---
 1
 4

The NULL element is lost in the second case, which is unwarranted as far as
I can tell.

Tested with the latest PostgreSQL 9.1.9 and 9.2.4. Identical results.

I presented the case with more details in this question on Stackoverflow:
http://stackoverflow.com/questions/16452501/null-emements-lost-when-casting=
-result-of-unnest

Accompanied by this demo on SQLfiddle:
http://www.sqlfiddle.com/#!12/d41d8/930

As advised by Pavel, I am reporting this as possible bug now.

Regards
Erwin