Has anyone ever seen this situation.  I have a custom, published
appointment form with two user-defined fields (defined both on the
custom form, and in the folder); in my vsto add-in code, I am setting
these value via the ItemProperties collection (not UserProperties
collection).  In the case of a recurring appointment, I iterate thru
all the occurrences, and set the values of these 2 properties, inside
the Write event.  So far so good.  But when I go to look at the series
in the calendar view, I have 2 unexpected (and bad) things:

1 - on all the occurrences except the master, the subject is not
displayed; it just shows the time.
2 - if I try to open any single occurrence (except the master), the
item is apparently one-off because I get the "malicious code" dialog,
and some controls in my form (e.g. ListView) are not displayed.

Looking at one of these one-off appointments in the debugger, I can
view those user-defined properties (via the ItemProperties) and they
are populated as expected.  I use only ItemProperties collection,
never UserProperties.

I can still open the master appointment with no problem (it does not
appear to be one-off), and all my controls load fine, and the 2 user-
defined properties are there and populated as expected.

What could be causing this?

Thanks,
John