Tom, thanks for bringing up this issue. It is indeed a problem when you turn off parental control as a whole (not so if you simply turn off for a particular profile). This is fixed in v1.21, available now. Click the Check for Updates button in the System Settings page to update.
You need to name your devices first before they can be added to a profile. Click on the Status button to bring up the Status page that displays a list of connected devices. Named devices will display in blue, while unnamed devices will display in gray. Click on the host name to give the device a name. After that you can add the device to a profile. Other users asked similar questions, so we added some additional messages (in v1.21) to the “no devices to add” dialog to make it more informative.