Subscribe by Email not sending e-mails for multiple categories

I've been using Subscribe by Email and began receiving complaints that the newsletter was not being sent out. When I checked the plugin, the e-mails failed (said "User content empty") when there were posts with multiple categories even when both of those categories were selected to say they should send out updates. They were parent/child categories, if that makes any difference.

I'm using the latest version of wordpress and the latest version of the plugin. Is this a known issue or am I doing something incorrectly?