Interesting. Maybe will get addressed in the upcoming beta? It sounds like a lot of MAPI enhancements are slated. 

@Michael: Unfortunately this is one we can't reproduce from test clients here in a variety of scenarios, and so this isn't likely to get resolved though it is possible. Essentially what we're seeing is what looks like an intermittent DNS or connectivity failure resulting in the alias expansion failing, that or, a local conflict or address book issue in Outlook is preventing the alias expanding as expected. We've tested with similar DNS setups, versions, operating system versions, and account configurations, all without luck in getting it to happen outside of their environment. The only other thing I can think of here is a GPO/machine policy difference we're not aware of. I'd suggested posting here in case others have experience similar issues or might know how to track this down a little better. 

I'll try in our environment and see if we can replicate to help.

Thanks so much! To recap, there are specific aliases that fail to load like this, while most of them work as expected. The aliases in question also contain aliases themselves, which may contain further aliases in turn. So, this is a pretty complex alias setup in this case.

Just a quick follow-up for you on this! Kiswire was able to provide me a video that helped me reproduce this here using their accounts. If you click the TO field and use the GAL list, scroll down and add the alias - it expands fine. If you search for it (enter the first three letters) instead, it does not expand properly. I can't reproduce this with a similar setup on our own domain, so I do think its specific to their alias configurations and you likely won't be able to reproduce it unfortunately. If you can though please submit a ticket so we can collect more data for development. Thanks for the help Michael!