Does ROS publish random values to its joints when launched ?

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Hello,

I am trying to run a robot by first launching it on gazebo and then later running the plugin to control it autonomously in another tab of the terminal. Initially when I launch the robot in gazebo using this following command

roslaunch spider_gazebo spider_world.launch

The robot gets successfully spawned in gazebo in the desired world along with loading all the position controllers for all the joints and joint_state_controller. Immediately after robot is spawnned and all the controllers are loaded, robot starts moving its joints which means it keeps updating its joint positions with random values. I can not understand this behaviour, can anyone please help me with this ?

for reference, I would like to provide the code about how i added controllers ,

<transmission name="tran1_1">
<type>transmission_interface/SimpleTransmission</type>
<joint name="joint_1_1">
  <hardwareInterface>PositionJointInterface</hardwareInterface>
</joint>
<actuator name="motor1_1">
  <hardwareInterface>PositionJointInterface</hardwareInterface>
  <mechanicalReduction>1</mechanicalReduction>
</actuator>
</transmission>

and this is how i added controller to gazebo ,

joint_1_1_position_controller:
type: position_controllers/JointPositionController
joint: joint_1_1
pid: {p: 100.0, i: 0.1, d: 0.0}

can anyone please help me clarify this or provide me related webpage where this is explained ? I have gone through ros-control page multiple times but i still can not understand the following problem. Thank you