I am trying to implement Zimbra in a small office environment, and I want to populate each user's calendar with their work schedule, similar to what's mentioned in this thread. Each user is subscribed to their own remote .ics file. Since the schedules are modified by an external PHP webapp, I have the webapp call syncFolder on the user's remote calendar folder each time their schedule is modified.

Now here is my problem: I've noticed that each time syncFolder is run, the user's mailbox size increases by about 15kb, even when there is no change in the .ics file, which is only about 4kb. Any idea why this might be happening? (I've been looking for a way to find out what folder or part of the mailbox is actually been increasing, but haven't been able to find anything on that.)