Exchange 2010 users can't load resource on OWA 2013 CU2

Hello,

I'm on Exchange 2013 transition. I've upgrade Exchange 2010 SP3 to Exchange 2013 CU2 (co-existing).

Once I change DNS to CAS 2013, I found an issue :

If 2010 users access their mailboxes on OWA 2013. They can't download OWA resource(after proxy),like this photo

  However there is a joke story, after I fail to log on my 2010 mailbox on 2013 OWA. So I try to logon 2013 mailbox on 2013 OWA (certainly it works collect). And I go back to log on my 2010 mailbox again, it works collect!!!!)

  In conclusion, if the client used to log on 2013 mailbox on OWA 2013, the problem won't occur anymore.

But if the client has never used to log on 2013 mailbox, users can't log on their 2010 mailbox(like photo above)

So I don't know this issue is a bug?

Any suggestion?