We weren't copying the comments field from the calendar structure into the river. We only do it when the comments are non-empty. Saves a little space.
Before reading the lists, we loop over the feedsArray, emptying the list of lists for each feed. Otherwise there is no way for a feed to leave a list.
Also a good resource for River4 development is riverjs.org. It has links to examples, and the only documentation for river format that I'm aware of.