Hm, my experience and others' says it
should work.
So I'd suggest trying to isolate the problem to either you or the server. My first step would be to create a new account in MacOS, then set up iCal within that account. If it works, then you might have some corrupted iCal data. Or you could just delete all your local ical data. I think I posted a list of places to look. I'll edit this message if I find it.
If not, you could ask your sys admins to create a test account, and so forth.
Also, if you have iSync connector, then your site has a Zimbra Professional license, which gives them access to Zimbra support.
BTW the appended forward slash you mention in your post is normal.
EDIT: here's the post where I was able to solve a problem by deleting a bunch of stuff in a Mac account:
http://www.zimbra.com/forums/isync-c...tml#post154462