How often do you cache entries for these tests?
It usually depends on the initial TTL you set for your record. sometimes cache needs flushing, so if it was 86400 then wait a day. If it was significantly lower like 300, and its been >300 since making the change, email ipv6@he.net and see if they can flush cache.
I emailed em to ask if they can flush it..
Because it's still showing the wrong servers.. LOL