Bug in grep when using both --after-context and --invert-match

[Oni Studio]

Hi there,

I was working on a way to exclude 4 lines from a bind configuration file 
using grep.
However i might have found a bug trying to use both --after-context and 
--invert-match at the same time.

The following command produces the proper file-selection which i would 
like to exclude from the given file:
grep -A4 'zone "domain.com' /etc/bind/zones

Logically, i tried:
grep -v -A4 'zone "domain.com' /etc/bind/zones > /etc/bind/zones.new

This did not produce the desired effect. Instead grep just outputs the 
entire file-content (without changes).
Is it a bug or an unsupported feature?

Im running grep (GNU grep) 2.5.1 on Debian Sarge (kernel : 2.6.8-2-686-smp)

Good luck,

Fili Wiese