I built a custom theme that uses several custom fields in posts. Some add downloadable images, others parse YouTube videos. Everything seems to work fine (authors can create, edit, save, and delete information from these fields) and we haven't had any major problems.
Then one day all of the data disappeared. It was spontaneous, and not linked to any plug-in or core updates. The data in the custom fields for several posts simply vanished.
Has anyone else seen this behavior? What could be causing it?