Bitmask VPN blockes IPv6 enabled sites

I noticed a weird behaviour with bitmask vpn. I'm using the new debian packages. VPN works smooth using bitmaskclt (YEAH!), but IPv6 enabled sites are blocked, i.e ix.de. Before starting the VPN ix.de resolves for me to a IPv4 address. After starting the VPN it resolves to a IPv6 address, and ping packets are blocked.

To make it even weirder, I can navigate the site in the browser (browsers seem to rely on their own DNS resolver, not the systems one).

--- ~ » ping -c 1 -W 2 ix.de 
PING ix.de (193.99.144.80) 56(84) bytes of data.
64 bytes from redirector.heise.de (193.99.144.80): icmp_seq=1 ttl=250 time=48.5 ms

--- ix.de ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 48.513/48.513/48.513/0.000 ms
--- ~ » bitmaskctl vpn start
result    started
--- ~ » bitmaskctl vpn status
status      on
firewall    on
vpn         on
domain      demo.bitmask.net
↑↑↑         13.7 K
↓↓↓         4.7 K
--- ~ » curl -s ipinfo.io
{
  "ip": "46.165.242.166",
  "hostname": "tor.bitmask.net",
  "city": "Nusttal",
  "region": "Hesse",
  "country": "DE",
  "loc": "50.6333,9.8500",
  "org": "AS28753 Leaseweb Deutschland GmbH",
  "postal": "36167"
}%                                                                                                                                                   --- ~ » ping -c 1 -W 2 ix.de
PING ix.de(redirector.heise.de (2a02:2e0:3fe:1001:302::)) 56 data bytes

--- ix.de ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms


--- ~ » ping -c 1 -W 2 bitmask.net
PING bitmask.net (199.119.112.150) 56(84) bytes of data.
64 bytes from 199-119-112-150.i95.net (199.119.112.150): icmp_seq=1 ttl=55 time=123 ms

--- bitmask.net ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 123.930/123.930/123.930/0.000 ms