[derekr]

Spent a fair amount of time working on this this morning — was unsure if the problem was within the WebDAV server or with iCal & Keychain Access.

It turns out it's with iCal. If iCal has two calendars with the same filename, it will, basically, get confused. Looking at error logs, iCal was sending the wrong username and password to the server for authentication.

It looks like the best workaround would be modifiable names for the calendars. (I'll add a feature request.)