I've reviewed the code (0.8.63). It works correctly, but the contents of the custom column are added only if there's a value in the custom column.
In other words, if you have a custom column whose lookup name is fandom1, and the column is empty, then nothing is added to the jacket template.
To review the steps for adding the contents of a custom column to a book jacket:
- Go to Preferences|Advanced|Miscellaneous. Click the Open calibre configuration directory button.
- Within your configuration directory, navigate to (or create) a subdirectory resources/jacket
- Go to your calibre program directory, navigate to the resources/jacket folder.
- Copy stylesheet.css and template.xhtml from resources/jacket in calibre's program directory to resources/jacket in your configuration directory.
- Edit the copy of template.xhtml in your configuration directory to add a custom column. The instructions are in a comment at the end of the file.
- Convert the book, selecting Insert metadata as page at start of book in the Structure Detection section of the Conversion dialog.