I am having the same exact problem with 13-13 on Ubuntu 18.04 installed on bare metal. Like the OP, the parking module is the only one I am having trouble with. I'm trying to change 45 seconds to 300.
Having this exact same issue on two separate builds, same story. Ubuntu 18.04.2 installed on bare metal, grabbed the 13-13.10 installer script. Can't seem to save settings in the webGUI for the parking module either.