Unwanted prefix getting added to CMAKE_PREFIX_PATH

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Hi, I am using ROS Indigo. The problem is very simple. I unset the CMAKE_PREFIX_PATH variable. I source /devel/setup.bash. I get an unwanted prefix /home/<user-name>/devel added to my CMAKE_PREFIX_PATH.

echo $CMAKE_PREFIX_PATH
/home/<user-name>/devel:/home/<user-name>/catkin_ws/devel:/opt/ros/indigo

I didn't do any changes to devel/setup.bash or devel/setup.sh. What could be the cause? and How to avoid it?

Thank you.