Model is valid only if not saved as "model.sdf"!!

edit

I am using "gz sdf -p <file>" (or with "-k") to check the validity of a model. I was always getting errors, even when I removed pretty much everything from my model. I ended up with just the following, but still without a successful validation:

<?xml version='1.0' ?>
<sdf version='1.6'>
  <model name='forklift'>
    <!-- Base/Support link -->
    <link name='base_link'>
      <pose>0 0 0 0 0 0</pose>
      <inertial>
        <pose>0.237624 0 0.122112 0 0 0</pose>
        <mass>0.100</mass>
        <inertia>
          <ixx>0.00101506</ixx>
          <ixy>0</ixy>
          <ixz>-2.93069e-05</ixz>
          <iyy>0.00107209</iyy>
          <iyz>0</iyz>
          <izz>0.00105703</izz>
        </inertia>
      </inertial>
      <collision name='base_link_collision'>
        <pose>0.24 0 0.123333 0 0 0</pose>
        <geometry>
          <box>
            <size>0.06 0.2 0.06</size>
          </box>
        </geometry>
      </collision>
      <visual name='base_link_visual'>
        <pose>0.24 0 0.123333 0 0 0</pose>
        <geometry>
          <box>
            <size>0.06 0.2 0.06</size>
          </box>
        </geometry>
      </visual>
      <gravity>1</gravity>
      <velocity_decay/>
    </link>
  </model>
</sdf>

The strange thing is, if I save this as anything but "model.sdf", it says it is valid. If I save it as "model.sdf", it says it has errors (although they do not include any relevante information, as stated in https://bitbucket.org/osrf/sdformat/i... ).

Any ideia why is this?