I have a user on a zcs 6.0.2 who cannot see the "to:" field information in the default reading pane view of the web client. In on other words, the subject is there, the sender is (usually, but not always, I think) there, and the word "To:" is there, but the actual recipient address of the "to:" field is absent. If the message's source is viewed, the "to:" information can be seen. If the message is opened in it's own window, the "to:" information can be seen.
Other users on the same installation do not seem to be experiencing this symptom.
I've tried already re-indexing the mailbox, which was the first time I've ever done that. I am not sure it really did anything as it appeared as if the re-index finished almost immediately and the status seemed to indicate that 0 messages were indexed. In any event, this attempt didn't change any thing for the user.