Teams uses EWS-API wrong which leads to wrong timezone in meetings

Schnittlauch 

So after a while debbuging with MS support we still have no solution. But we know what's happening. Or we think we know. Who knows? 🙂

1. Meeting created in Teams (Teams Online, Web-Browser)

a) Teams-Online uses SMTP to send the meeting to the external user over our hybrid environment (mail-flow). The meeting shows itself correct inside the external calender, because the meeting uses UTC+1 or Western Europe Standard (CET). The meeting isnt "changed" in anyway over the SMTP-flow.

b) Teams-Online uses EWS to write the meeting into the local users calender. The meeting shows itself correct, because the OWS-settings of the user are configured to UTC+1. But the meeting itself is created "incorrect". That leads to the bug we see.

Teams-Online puts the meeting with UTC to the EWS-API, although the user created it with UTC+1. We think that's the problem.

2. Changing the meeting with OWA in Exchange On-Premise

The meeting is internaly saved as UTC. See 1.b) Updating the meeting sends an update to the external user. The base is UTC, instead of UTC+1. So we have a missmatch for the external user. The internal user still sees the meeting correct, because their local enviroment is set to UTC+1.

So does anybody know if there is a setting for the timezone?? somewhere teams ignores the correct timezone, when adressing the EWS-API? The user-settings (myprofile.microsoft.com), using Teams-Online are set to UTC+1. The meeting is created with UTC+1 within Teams-Online. We looked at the clients timezone-settings. Those we also set to UTC+1/CET. But EWS uses UTC. 

Can some look how their meetings are created through EWS using the Web-Client of Teams. Using the Teams-App on iOS shows the same problem. It should be something between the "Cloud" and our "Hybrid" environment.

Attached you find a screenshot of the EWS-debugger. You see a meeting created by Teams-Online for 14:30 (UTC+1) written through EWS to Exchange On-Premise.