Double fault, instant reboot

[miloman]

running nanobsd 2.1 from an sd-card on a shuttle ds47.

it runs 100% stable when pushing normal tcp packets aka web browsing etc. but when i try to move packets through an ipsec tunnel i get this error: http://imgur.com/p3nk9OL

ping through the tunnel works fine 421 out of 421 packets sent/received without a problem.

any ideas?