After some time. I'm playing around with MATLAB ROS again (http://www.mathworks.com/hardware-support/robot-operating-system.html).

When I try to create a node in Matlab using Node = rosmatlab.node('Test','http://129.10.113.238:11311');

This results in the following output:

Environment variable ROS_IP does not match localhost's IP address

However, when I check ROSMASTERURI and ROS_IP, they have the correct values (in both the Ubuntu terminal and the Matlab command line).