Currently Being ModeratedMar 21, 2013 6:20 AM (in response to Moritz-Alexander Lebrecht)
Since you are showing more than 1 of the same user, I imagine that you have the open directory bridge 'Search for user accounts' enabled in the AB service.
The ? symbol is normal when iCal doesn't know where to lookup the user's free/busy details.
On the client side, perhaps 1 AB entry contains the info needed and the other doesn't.
Instead of typing the name in ical attendees, try dragging the entry from AB.
Try one occurence of a user, then the other occurence of the same user.
I'm thinking when you let ical choose, its grabbing the incomplete entry in some cases..
this might not be the solution, but hopefully puts you on a path towards it :-)