Alexa Group Endpoint - Change Color => Brightness goes 100%

i want to control a hue-group (zone or room) over openHAB3 (OpenHABian) and Alexa.
Its working good so far but i have a small issue… When i set the color, the brightness of the group goes to 100%.
When changing the color temperatur. This is not an issue, the brightness stays the same.
I tried 2 different configurations. Both with the same result.

Nr1

Group Gr_HueBuero_Zone "Büro Hue" (hue) {alexa="Endpoint.Light"}

Switch   HueBueroSwitch             "Schalter"        (Gr_HueBuero_Zone) {channel="hue:group:001788288b39:2:switch", alexa="PowerController.powerState"}

Dimmer   HueBueroColorTemperature   "Farbtemperatur" (Gr_HueBuero_Zone)  {channel="hue:group:001788288b39:2:color_temperature", alexa="ColorTemperatureController.colorTemperatureInKelvin"}

Dimmer   HueBueroBrightness         "Helligkeit"      (Gr_HueBuero_Zone) {channel="hue:group:001788288b39:2:brightness", alexa="BrightnessController.brightness"}

Color    HueBueroColor              "Farbe"          (Gr_HueBuero_Zone)  {channel="hue:group:001788288b39:2:color", alexa="ColorController.color"}

String   HueBueroAlert              "Alarm"           (Gr_HueBuero_Zone) {channel="hue:group:001788288b39:2:alert"}

String   HueBueroScene              "Scene"           (Gr_HueBuero_Zone) {channel="hue:group:001788288b39:2:scene"}

Nr2.

> Group Gr_Flur_Room "Flur" (hue) {alexa="Endpoint.Light"}
> 
> Switch   FlurRoomSwitch             "Schalter"    (Gr_Flur_Room)     {channel="hue:group:001788288b39:8:switch"}
> 
> Dimmer   FlurRoomColorTemperature   "Farbtemperatur"  (Gr_Flur_Room)    {channel="hue:group:001788288b39:8:color_temperature", alexa="ColorTemperatureController.colorTemperatureInKelvin"}
> 
> Dimmer   FlurRoomBrightness         "Helligkeit"    (Gr_Flur_Room)      {channel="hue:group:001788288b39:8:brightness"}
> 
> Color    FlurRoomColor              "Farbe"          (Gr_Flur_Room)     {channel="hue:group:001788288b39:8:color", alexa="BrightnessController.brightness,PowerController.powerState,ColorController.color"}
> 
> String   FlurRoomAlert              "Alarm"          (Gr_Flur_Room)     {channel="hue:group:001788288b39:8:alert"}
> 
> String   FlurRoomScene              "Scene"         (Gr_Flur_Room)      {channel="hue:group:001788288b39:8:scene"}

Could you please include a request utterance example and the command received from that request in your OH event logs?