Wrong brightness when I use RGB and W on RGBCW bulb

[itec78]

Hello.
I have RGBCW bulbs.
When I control them with HA and I switch from white (cold-warm) mode to RGB mode, brightness changes in wrong way.
HA shows brightness change, but bulb doesn't change brightness, only color.
If I create a new scene and I set bulb to warm white the bulb changes accordingly. But when I use that scene, the bulb is set to color (I think it remembers last setting)
What's wrong?