.dae/.stl meshes repels each other, when standart box do not.

I want to robot laid tower of cubes. When I use simple models of cubes, they lie on each other. 1 1 1 But if I use cubes of .dae or .stl they begin to repel each other and the tower collapses. 1.0 file://media/models/cube.stl file://media/models/cube.dae I've tried to add [inertia] and [collision] -> [surface] properties, but it doesn't help. What am I missing?