STP is no solution. Did you try enabling the bridge loop avoidance ? http://www.open-mesh.org/wiki/batman-adv/Bridge-loop-avoidance
You might need to upgrade to a later batman-adv version though.
Regards, Marek
We did not enable bridge loop avoidance, IIRC we did not run batman on the bridge interface due to overhead on the vpn links.
But we'll enable it on the nodes we have access to.
thx bjo