Adding geometry_msgs/Pose caused geometry_msgs/Twist value to change [rosserial]

edit

This is what I have tried,

1) Creating a msg file as shown below:

robo_base/Encoder enc
geometry_msgs/Twist twist

2) Generate the header files for catkin_ws/devel/include and ros_lib, build the package and stuffs

3) When I launch the nodes and rostopic echo /robo_data (What I named it), I got the velocity at around 0.27ish m/s (Joystick control, max is 0.25).

4) Then, I tried again by adding a new line into the message file:

robo_base/Encoder enc
geometry_msgs/Pose pose
geometry_msgs/Twist twist

5) Repeat step 2 and 3, now the velocity turned into 0.34ish (Nothing changed in the joystick files, should stayed somewhere around 0.25).

May I know what is causing the error above or does anyone knows any fix for it? Thanks.