I didn't observe this exact thing, but I've seen some weird traceroute outputs on a Windows box behind a Comtrend ADSL router. The PTRs returned were completely wrong and I think there were some other issues too.
Once we replaced the CPE everything went back to normal, so I'd check that first, maybe it's doing something funny to the IPv6 traffic.
Best regards
Tomáš Hetmer
> From: alexandre.abreu@vodafone.com
> To: ripe-atlas@ripe.net
> Date: Tue, 21 Jul 2015 08:51:41 +0000
> Subject: [atlas] 1msec RTT to ipv6.google.com?
>
> Hi all
>
> Anyone had any issues with wrong RTTs on IPv6 probes? I've setup a ping probe (ID#2143865) to ipv6.google.com and it's consistently giving 1msec RTT on the seismograph and the json file. It is physically impossible. This is the RTT I get on the CPE the probe is connected to:
>
> SEQ HOST SIZE TTL TIME STATUS
> 0 2a00:1450:4003:806::200e 56 59 12ms echo reply
> 1 2a00:1450:4003:806::200e 56 59 12ms echo reply
> 2 2a00:1450:4003:806::200e 56 59 12ms echo reply
> 3 2a00:1450:4003:806::200e 56 59 12ms echo reply
> 4 2a00:1450:4003:806::200e 56 59 12ms echo reply
> 5 2a00:1450:4003:806::200e 56 59 12ms echo reply
>
> Regards,
> Alexandre Abreu
>