Bones don't work as expected

Hi everyone!

I’m just joining this 2d world, and I’m learning to use Synfig.
Following the manual, I’m now in that lesson, which teaches about Bones:

The problem is: I created the arms, using spline, and as followed by the tutorial, I linked all the vertices of each part into the respective bone. But when I tried to move the bones, the forms are moved in a weird way: It seems the part is rotating in a different center point, detatching from the arm.

I created also, three squares and tried to apply bones as well, but instead of rotating in a different center point, the outline moves as expected, but the region not.

What I did wrong?
SynfigAnimation_Bones.sifz (9.12 KB)