Hosted Exchange & iCal - can't add shared calendar

I am having a problem with my Hosted Exchange account and iCal. Prior to the widespread issues with Hosted Exchange and Mac Mail in late March/early April, I was able to add shared Exchange calendars in iCal by going to Preferences-Accounts-Delegation, clicking the + and typing in the first few characters of a colleague's email address (a colleague who has shared their calendar with me). I have four shared calendars right now that are working perfectly, I can see their appointments and the shared calendars update when changes are made.

The problem is that I can't add a new shared calendar using this method. I have three new employees whose calendars I need to add to iCal and the process to add a shared calendar is not working. I type the first few characters of their email address like I did before and nothing happens. I have tried (on another Mac) to delete the account and re-add it, I can't add any shared calendars there so I've lost the four that I had before and can't get them back.

I have verified that this is working fine in Outlook 2010 on a virtual PC, it appears to be another problem with Hosted Exchange that is crippling Mac productivity.

Anyone else seeing this problem?