Regenerating collision matrix does not work on existing package

[pirobot]

In version 0.4.3-alpha under ROS Groovy and Ubuntu 12.014, clicking on the "Regenerate Default Collision Matrix" button in the Setup Assistant after loading an existing package does not correctly update the collision matrix. It appears that the matrix is not being initially "zeroed out" before recalculation since it does work properly if all collision lines are first manually deleted from the SRDF file.