(Zimbra support case 00048097; local WHD 5134)

So I've got iCal 3 (OS X 10.5.8) dying on specific shared calendars with "http://1.1.400 bad request to cal.davqueueqbleacctoperation fail."

I found the 400 errors in jetty/logs/access_log.2010-01-08: - - [08/Jan/2010:18:35:08 +0000] "REPORT /dav/test/Test%20User's%20Calendar/ HTTP/1.1" 400 0 "-" "DAVKit/3.0.6 (661); CalendarStore/3.0.8 (860); iCal/3.0.8 (1287); Mac OS X/10.5.8 (9L31a)"

And mailbox.log (strangely 10 seconds behind, after time zone correction):

2010-01-08 12:35:18,329 WARN ... dav - proxy request failed 
org.dom4j.DocumentException: Error on line 1346 of document : Character reference "&#0" is an invalid XML character. Nested exception: Character reference "&#0" is an invalid XML character.
at org.dom4j.io.SAXReader.read(SAXReader.java:350)
at org.dom4j.io.SAXReader.read(SAXReader.java:264)
at com.zimbra.cs.dav.service.DavServlet.isProxyRequest(DavServlet.java:583)
at com.zimbra.cs.dav.service.DavServlet.service(DavServlet.java:221)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
2010-01-08 12:35:18,374 INFO ... dav - sending http error 400 because
: requested resource is not a calendar collection
Line 1346 of what?

The literal string &#0 does not appear in the .ics export of the calendar. I do see another escape, lots of color="#000000" in embedded HTML, and some binary (hopefully unicode) gunk embedded in Outlook-originated messages.