[O] "S:" prefix when syncing via CalDAV

[John Morrissey]

I'm syncing to Nextcloud via CalDAV with org-mode 9.0.3 and the latest
org-caldav.

Events are sometimes synced (and modified in the .org file) with the prefix
"S:". The symptoms are exactly like:

  https://github.com/dengste/org-caldav/issues/33#issuecomment-74551937

  "The SCHEDULED time gets converted to an active timestamp and a freshly
  created property drawer with a new id is inserted above that newly created
  active timestamp."

It looks like this prefix is being prepended by org-icalendar-entry in
ox-icalendar, but I don't know enough about Lisp or org internals to debug
much further.

Here are my org-{icalendar,caldav} settings:

  (setq org-icalendar-alarm-time 30)
  (setq org-icalendar-use-deadline '(event-if-todo event-if-not-todo todo-due)
        org-icalendar-use-scheduled '(event-if-todo event-if-not-todo 
todo-start))
  (setq org-export-exclude-category (list "dummy"))

  (setq org-caldav-inbox (expand-file-name "~/org/caldav-inbox.org"))
  (setq org-caldav-files org-agenda-files)
  (setq org-caldav-show-sync-results nil)
  (setq org-caldav-resume-aborted 'never)

Is there some configuration I need to change to stop this behavior?

-john