add_header directive not working for 40x and 50x responses

[fxdemolisher]

As per the http header module's documentation (link) the add_header directive does not work for 40x and 50x error pages. 

Is there a specific reason for this? Will the ability to use this directive in error pages be added later on?

This is something that is required by my project since NGINX is responsible for serving error pages and we need to set specific cookies when the error page is displayed.

There is also a post on the ruby nginx forums (link) with this issue without a satisfactory answer.

Any information on the issue would be appreciated.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,11280,11280#msg-11280