MuJoCo parsing bug

cartpole.urdf

<?xml version="1.0" encoding="utf-8"?>
<!--Create with rod using build_cartpole_model.py -->
<robot name="cartpole"> 
    <link name="world"/> 
    <link name="rail"> 
        <inertial> 
            <origin xyz="0.0 0.0 1.2" rpy="1.5707963267948963 0.0 0.0"/> 
            <mass value="5.0"/> 
            <inertia ixx="10.416697916666665" ixy="0.0" ixz="0.0" iyy="10.416697916666665" iyz="0.0" izz="6.25e-05"/> 
        </inertial> 
        <visual name="rail_visual"> 
            <origin xyz="0.0 0.0 1.2" rpy="1.5707963267948963 0.0 0.0"/> 
            <geometry> 
                <cylinder radius="0.005" length="5.0"/> 
            </geometry> 
        </visual> 
        <collision name="rail_collision"> 
            <origin xyz="0.0 0.0 1.2" rpy="1.5707963267948963 0.0 0.0"/> 
            <geometry> 
                <cylinder radius="0.005" length="5.0"/> 
            </geometry> 
        </collision> 
    </link> 
    <link name="cart"> 
    <inertial> 
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/> 
        <mass value="1.0"/> 
        <inertia ixx="0.0035416666666666674" ixy="0.0" ixz="0.0" iyy="0.0010416666666666669" iyz="0.0" izz="0.0041666666666666675"/> 
    </inertial> 
    <visual name="cart_visual"> 
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/> 
        <geometry> 
            <box size="0.1 0.2 0.05"/> 
        </geometry> 
    </visual> 
    <collision name="cart_collision"> 
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/> 
        <geometry> 
            <box size="0.1 0.2 0.05"/> 
        </geometry> 
    </collision> 
    </link> 
    <link name="pole"> 
        <inertial> 
            <origin xyz="0.0 0.0 0.5" rpy="0.0 0.0 0.0"/> 
            <mass value="0.1"/> 
            <inertia ixx="0.008333958333333334" ixy="0.0" ixz="0.0" iyy="0.008333958333333334" iyz="0.0" izz="1.25e-06"/> 
        </inertial> 
        <visual name="pole_visual"> 
            <origin xyz="0.0 0.0 0.5" rpy="0.0 0.0 0.0"/> 
            <geometry> 
                <cylinder radius="0.005" length="1.0"/> 
            </geometry> 
        </visual> 
        <collision name="pole_collision"> 
            <origin xyz="0.0 0.0 0.5" rpy="0.0 0.0 0.0"/> 
            <geometry> 
                <cylinder radius="0.005" length="1.0"/> 
            </geometry> 
        </collision> 
    </link> 
    <joint name="world_to_rail" type="fixed"> 
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/> 
        <parent link="world"/> 
        <child link="rail"/> 
    </joint> 
    <joint name="linear" type="prismatic"> 
        <origin xyz="0.0 0.0 1.2" rpy="0.0 0.0 0.0"/> 
        <parent link="rail"/> 
        <child link="cart"/> 
        <axis xyz="0 1 0"/> 
        <limit effort="500.0" velocity="10.0" lower="-2.4" upper="2.4"/> 
    </joint> 
    <joint name="pivot" type="revolute"> 
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/> 
        <parent link="cart"/> 
        <child link="pole"/> 
        <axis xyz="1 0 0"/> 
        <limit effort="500.0" velocity="10.0" lower="-3.4028234663852886e+38" upper="3.4028234663852886e+38"/> 
    </joint>
</robot>