Exchange 2013 and OWA 2013 customization

Hi all

In OWA 2013 we try to manage customization in UIExtensions.xml as in previous Exchange 2010 OWA version.

Problem is that any new entries in <SmallIconMappings>, <RightClickMenuExtensions> and <NewItemMenuEntries> are not accepted by OWA.  Is there something new on background what needs to be set/changed to allow OWA work with this customization?

Any advise?

Thanks!

cciapocka