[Q] problems with calendar invitations in mail client topic

I've recently updated my Galaxy S5 to Android 5.0 (stock rom!). So far all is working fine, with one exception: I've set up an active sync connection in the samsung mail client to our company-mailserver (Exchange 2013), and I can get all mails, calender, contacts and so on... but when I receive a calendar-invitation I cannot open it! I also cannot open accept-notifications in my inbox on Android (from calendar-invitations which I've send out using Outlook on my PC). This is very bad for me, and so far the only bug I've found in my device. Just to be complete: I've used Touchdown as mailclient on Android in the last couple of years, and I've decided to switch to the stock-mailclient because of the clean interface in material-design here - in comparisation the interface of Touchdown is "historical".

can anyone help me out with my problem?

many thanks
Gerald