Fixed joint moving when grasping

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I have fixed joint in my arm joining the shoulder to world, but this joint moves around when I am trying to grasp an object. The entire urdf is here.

The important part is

<!-- Left arm -->
<link name="left_base"/>
<!-- First element of the arm fixed to the parent -->
<joint name="left_base_leftarm__base_joint" type="fixed">
    <origin rpy="-1.570796327 -1.570796327 0" xyz="0.045 0.1665 1.526"/>
    <parent link="left_base"/>
    <child link="leftarm_shoulder_link"/>
</joint>

<link name="world"/>
<joint name="world_left" type="fixed">
    <parent link="world"/>
    <child link="left_base"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
</joint>
<joint name="world_right" type="fixed">
    <parent link="world"/>
    <child link="right_base"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
</joint>
<joint name="world_stand" type="fixed">
    <parent link="world"/>
    <child link="base_link"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
</joint>