[Zope] Calendar Tag & Zope 2.3 and higher: Invalid or duplicate property id

[Kees de Brabander]

I've been using the Calendar tag since zope 2.1.6. In the process of
upgrading to Zope 2.4.3 I found the calendar tag does not work anymore. If I
try to edit a date property, I get a Bad Request error, value: Invalid or
duplicate property id. Traceback see below. I've been experimenting a bit
and created an example faithfully following the Jon Udell How-to. I imported
this example in different versions of zope. The incompatibility with the
calendar tag gets to the surface somewhere after 2.2.
Did nobody else experience this?
tiv,cb

Traceback (innermost last):
  File D:\Zope\243\lib\python\ZPublisher\Publish.py, line 223, in
publish_module
  File D:\Zope\243\lib\python\ZPublisher\Publish.py, line 187, in publish
  File D:\Zope\243\lib\python\Zope\__init__.py, line 226, in
zpublisher_exception_hook
    (Object: index_html)
  File D:\Zope\243\lib\python\ZPublisher\Publish.py, line 171, in publish
  File D:\Zope\243\lib\python\ZPublisher\mapply.py, line 160, in mapply
    (Object: editCalendarProperty)
  File D:\Zope\243\lib\python\ZPublisher\Publish.py, line 112, in
call_object
    (Object: editCalendarProperty)
  File D:\Zope\243\lib\python\Shared\DC\Scripts\Bindings.py, line 324, in
__call__
    (Object: editCalendarProperty)
  File D:\Zope\243\lib\python\Shared\DC\Scripts\Bindings.py, line 354, in
_bindAndExec
    (Object: editCalendarProperty)
  File D:\Zope\243\lib\python\Products\PythonScripts\PythonScript.py, line
363, in _exec
    (Object: editCalendarProperty)
    (Info: ({'script': <PythonScript instance at 01BE2670>, 'context':
<DTMLMethod instance at 01BDDD40>, 'container': <Folder instance at
01BD3D20>, 'traverse_subpath': []}, (), {}, None))
  File Script (Python), line 5, in editCalendarProperty
    (Object: guarded_getitem)
  File D:\Zope\243\lib\python\OFS\PropertyManager.py, line 320, in
manage_addProperty
    (Object: Agenda)
  File D:\Zope\243\lib\python\OFS\PropertyManager.py, line 243, in
_setProperty
    (Object: Agenda)
Bad Request: (see above)