After some further research, it seems that this issue is tied in with the guildbank mod. If the guild bank does not collect all information, when it uploads to the website, it erases your level, race, class from your information. When this is done, the calender removes you from the signup list because it cant associate a class to your toon that you signed up with.
Good call. That is right. I will be adding something like "Undefined Class" or something to accommodate those little bits.
It's worth noting that it only removes you from the list until you fix your class. When the class is restored, the signup will definitely reappear in the list.