physics objects (triangle mesh vs triangle mesh) falling through each other

Hi, I am a new user of SIO2 v 1.4.
I found a problem that two physics objects with triangle meshes (collision type) will fall through each other.
I did some experiments to make sure this problem:
(1) A cube with a cube by setting both of them as box collision types ---> OK to collide with each other
(2) A cube with a cube by setting one as triangle mesh and the other as box type --> OK to collide with each other
(3) A cube with a cube by setting both of them as triangle meshe collision types --> Fall through each other
(4) All other combinations are OK, too.

It seems only triangle mesh vs triangle mesh can't collide each other well!!
PS: BTW, i am using tutorial061/062 as my testing base project

thanks!!
Tim