[SOLVED] Strange behavior of Philips Hue color bulbs

I found a problem in my setup the other day regarding Philips Hue color bulbs and Philips hue binding (with hue bridge) which is as follows:
In rules and in HabPanel I’m setting the color item to a new HSB value. Openhab react as expected and indicates in event log that the the item has changed state.
However after a few seconds without interacting with the system there is a new state change with slighlty changed HSB values (see bold in logs below).
Any idea what can be wrong?

Example 1
2019-04-02 22:35:07.329 [nt.ItemStatePredictedEvent] - gustav_drawer_Color predicted to become 29,80,57
2019-04-02 22:35:07.332 [vent.ItemStateChangedEvent] - gustav_drawer_Color changed from 29,63,100 to 29,80,57
2019-04-02 22:35:16.996 [vent.ItemStateChangedEvent] - gustav_drawer_Color changed from 29,80,57 to 30,82,57

Example 2
2019-04-02 22:34:29.737 [nt.ItemStatePredictedEvent] - gustav_drawer_Color predicted to become 30,64,100
2019-04-02 22:34:29.739 [vent.ItemStateChangedEvent] - gustav_drawer_Color changed from 30,82,57 to 30,64,100
2019-04-02 22:34:36.908 [vent.ItemStateChangedEvent] - gustav_drawer_Color changed from 30,64,100 to 29,63,100

"predicted" comes from autoupdate, the openHAB feature that listens for commands and makes a guess about the effect on the Item.
The second line is that prediction being put in place by update.

autoupdate is enabled on each Item by default, and if you don’t like it you can disable it. That’s often a good idea if you are getting prompt feedback from an actual device.

The third line a short time later is the update from the binding that reflects the status of the actual device.
That’s likely to involve some scaling or transformation between steps 0-100 to 0-255 and so on, so I’m not surprised it may differ slightly from the command.