Field Collection: multi-entry, add another item takes forever SOLVED

Now that I've managed to track down the patch for this issue I realize that I probably wasted a lot of time trying to find alternatives to field collections, and even making a start on my own compound field type.

Had I thought to look at the report log earlier, I would have found the answer much more quickly. That's a lesson learned for me, but it seems pretty terrible to me that field collection has had a fix available for three months, but the maintainers have let the supposed stable version remain broken for everyone who wants multi-entry field collections.

Anyway, this is a marker to remind myself why I'm on the dev branch of field collections now.

The log message was `Warning: array_filter() expects parameter 1 to be array, string given in array_filter() (line 591 of /path/to/drupal/sites/all/modules/field_collection/field_collection.module).

UPDATE: This patch is finally in the latest stable beta branch.