Search Folders disappearing on each start of Outlook 2013

Hi,

after moving to Office 365 E1, my search folders disappear each time I start Outlook 2013. For example I create a new search forder 'unread Mail' and add it to the Favorites folder. When I close Outlook and reopen it, I can see the folder disappearing from both the Favorites folder and the 'search folder' folder.

I deleted my Outlook profiles and the \AppData\Roaming\Outlook folder but the problem persists. This obviously  affects all users.

Help!

Thanks
Florian