I'm also getting inconsistent test results. I'm using the Java tool from this site:
http://labs.ripe.net/content/testing-your-resolver-dns-reply-size-issuesSometimes it gives me the following results:
Announced buffer size: 4096 bytes
Measured buffer size: 3839 bytes
EDNS enabled: yes
DNSSEC enabled: yes
And other times it gives me these results:
Announced buffer size: 512 bytes
Measured buffer size: 486 bytes
EDNS enabled: no
DNSSEC enabled: no
Is there something that could be causing this?