Calendar Event comment shows code not text

I have a new customer who is testing eM Client (v8.0.3385)
He is using an IceWarp v13 Server.

We discovered a major problem :

The comment of an Event shows on a mobile phone calendar (Android / Gmail Exchange) some “style sheet like” text before the actual text.

See attachment.

This happens only if we create the event in eM Client (German). No such problem with English eM Client.

Anybody know show we can prevent that ?

It is a show stopper at moment.