Well, that happens already if you send the command (ON, OFF, or a PercentType) to a OpenHAB group with Dimmer items in it:
All Dimmer items in the group will receive one command each.
So you have two options:
- Send command to the group - each items received the command - the TRADFRI binding sends the commands to the gateway. Sometimes the gateway can’t handle this, and some bulbs do not change. That’s sadly a limitation in the gateway.
- Send commands in a rule to every bulb, WITH a delay - higher chance that every bulb does what you want, but you have delays…
As the native group support is not ready yet, there is currently no other possibility, I think.