For the custom mood theme editor to save your changes, you need to check the "inherit from" check boxes, allow the URLs and mood theme pictures to appear, (the URLs appear uneditable and in red) and then uncheck each box so that the URLs turn black, before saving the changes. You can also paste the URLs of your mood pics in here directly, or just type in the name of the image file in the URL that's there already.
This information needs to be added, either to FAQ64 or to moodthemes.bml