You will have to use a sphere for one of them, or you will have to use some different collision engine than Panda’s. Perhaps ODE or Bullet will help here.
Panda’s own collision engine does not support polygon-polygon collision tests. Usually, you don’t want to do this anyway, because it’s so much more expensive than sphere-polygon or sphere-sphere, but if you really do need this, then you need something more powerful than the built-in collisions.
David