catkin+tmux problem
When I use catkin_make inside of a tmux session, and then source the devel/setup.sh, I sometimes end up with the CMAKE_PREFIX_PATH and the ROS_PACKAGE_PATH being backwards. This causes my overlay to be an underlay, so catkin finds system ROS packages before my source packages. It doesn't always happen, and I don't have a reliable way to reproduce it. Its possible that it isn't actually related to tmux, but I've only seen the problem when inside a tmux session.
I'm posting here in the hope that someone has some insight into why this happens.
Here's the issue for this on github: https://github.com/ros/catkin/issues/455