iStar DIM Light, z2m supported, devices in HA don’t work

[umtauscher]

Hi,
this is a mystery to me. The device is supported in z2m and published to MQTT. The Entities show up in Homeassistant, but the do not work. They don‘t show the state of the device and toggeling or setting the brightness doesn’t work either.
What am I missing here? Is this a bug or a feature.😉
What can I do?
TIA

[umtauscher]

Well let me be a bit more precise:
Toggle doesn‘t work.
switch on only works, when I give it a brightness also.
switch off works, but the icon state stays on.

[umtauscher]

I solved it myself. Setting the optimistic flag solved all my problems.
I don‘t understand what it does, but never mind.