I haven't downloaded and tried the Blender session you provided, but I'm going to assume you're using polygons with more than 3 sides. The SMD format itself only supports triangles, so any quads and other polygons with more than 3 sides will be converted into triangles on export. When importing, they will remain as triangles.

Another possibility is that you may be rigging vertices to less than or more than a sum of 1.0 when all bone weight values are added up. Or maybe you're using some modifiers that can't be exported/imported correctly.

OK. I solved this issue. This is a subsurf modifier with armature modifier.
But i am tried several other files with skeleton and animation.
Please explain how animate it in blender. When i animating in blender already is ok. But in imported SMD animation is wrong in several bones. Only legs are working, but no neck, shoulders, arms, etc. I am using model from MakeHuman program.

Can you tell me how animate in blender correctly?