Server: verified on both 5.0.6 and 5.0.8 (both NE).
Client: Apple iCal (latest updates) and Mulberry (behaviour in Mulberry is slightly different, read on for more info).

How to reproduce:
1) configure some calendars in your Zimbra webinterface, setup your CalDav client, make sure it's working, that you can see al calendars etc.
2) add a new calendar, with a special (non-ASCII) character in it (eg: "test with ").
3) Refresh the calendar list in iCal. ==> It won't show up in iCal (shows up as a calendar with an empty name in Mulberry)

Even worse:

4) Add a few new calendars, without special chars in the name.
5) Refresh the Calendar list ==> They won't show up either in iCal (they do show in Mulberry)

To prove my point:

6) Completely erase all data in your iCal, quit iCal, start it again and recreate the CalDav account. ==> Not a single calendar will show up.

7) Delete the calendar with an accented name in it in your Zimbra interface. Refresh the iCal list ==> They all show up again.

Can anyone confirm this and tell me if there is a fix? Thanks.

PS: Please note that adding UTF-8 data to the content of an appointment does seem to work, shows up fine, the error only happens when the name of the calendar contains non-ASCII chars in it.