Hi Simon
Following Joerg's comment I too have manually patched my tb8 lightening v1 with the patches above.

I haven't yet broken it, but can confirm the message Joerg sees.

transcript below  (good luck!)

CalDAV: itemUri.spec = https://p01-caldav.icloud.com/1428155234/calendars/91C0A18D-8889-44E2-8DB6-5774C9FCA6F2/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics
 ----------
CalDAV: send: BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/London
X-LIC-LOCATION:Europe/London
BEGIN:DAYLIGHT
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
TZNAME:BST
DTSTART:19700329T010000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
TZNAME:GMT
DTSTART:19701025T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20111104T111326Z
LAST-MODIFIED:20111111T141212Z
DTSTAMP:20111111T141212Z
UID:70aaeba9-9d4d-450b-bcf2-4bec2153094e
SUMMARY:New Event
DTSTART;TZID=Europe/London:20111111T120000
DTEND;TZID=Europe/London:20111111T130000
SEQUENCE:1
X-MOZ-GENERATION:1
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR

 ----------
CalDAV: recv: <?xml version='1.0' encoding='UTF-8'?><error xmlns='DAV:'><no-uid-conflict xmlns='urn:ietf:params:xml:ns:caldav'><href xmlns='DAV:'>/1428155234/calendars/home/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics</href></no-uid-conflict><error-description xmlns='http://twistedmatrix.com/xml_namespace/dav/'>(3303319186) Found component /1428155234/calendars/91C0A18D-8889-44E2-8DB6-5774C9FCA6F2/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics with same UID in a different collection: /1428155234/calendars/home/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics</error-description></error>
 ----------
Error: CalDAV: Unexpected status adding item to JB: 409
<?xml version='1.0' encoding='UTF-8'?><error xmlns='DAV:'><no-uid-conflict xmlns='urn:ietf:params:xml:ns:caldav'><href xmlns='DAV:'>/1428155234/calendars/home/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics</href></no-uid-conflict><error-description xmlns='http://twistedmatrix.com/xml_namespace/dav/'>(3303319186) Found component /1428155234/calendars/91C0A18D-8889-44E2-8DB6-5774C9FCA6F2/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics with same UID in a different collection: /1428155234/calendars/home/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics</error-description></error>
BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/London
X-LIC-LOCATION:Europe/London
BEGIN:DAYLIGHT
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
TZNAME:BST
DTSTART:19700329T010000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
TZNAME:GMT
DTSTART:19701025T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20111104T111326Z
LAST-MODIFIED:20111111T141212Z
DTSTAMP:20111111T141212Z
UID:70aaeba9-9d4d-450b-bcf2-4bec2153094e
SUMMARY:New Event
DTSTART;TZID=Europe/London:20111111T120000
DTEND;TZID=Europe/London:20111111T130000
SEQUENCE:1
X-MOZ-GENERATION:1
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR

 ----------
Warning: There has been an error reading data for calendar: JB.  However, this error is believed to be minor, so the program will attempt to continue. Error code: DAV_PUT_ERROR. Description: There was an error storing the item on the server.
 ----------
Error: An error occurred when writing to the calendar JB! Error code: MODIFICATION_FAILED. Description: Status Code: 409, Resource conflict.

<?xml version='1.0' encoding='UTF-8'?><error xmlns='DAV:'><no-uid-conflict xmlns='urn:ietf:params:xml:ns:caldav'><href xmlns='DAV:'>/1428155234/calendars/home/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics</href></no-uid-conflict><error-description xmlns='http://twistedmatrix.com/xml_namespace/dav/'>(3303319186) Found component /1428155234/calendars/91C0A18D-8889-44E2-8DB6-5774C9FCA6F2/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics with same UID in a different collection: /1428155234/calendars/home/70aaeba9-9d4d-450b-bcf2-4bec2153094e.ics</error-description></error>
Source file: resource://calendar/modules/calUtils.jsm -> file:///C:/Users/John/AppData/Roaming/Thunderbird/Profiles/1hzpmwy6.default/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calCalendarManager.js
Line: 1101
 ----------
Warning: Use of getAttributeNode() is deprecated. Use getAttribute() instead.
Source file: chrome://calendar/content/calendar-error-prompt.xul