White Series Dimmer (VTM31-SN) ignores brightness commands in HomeKit motion automations

[ryan]

The dimmer works normally for manual control, HomeKit slider control, and scheduled automations. But when triggered by a motion automation, it ignores the brightness value and turns on to the last brightness level instead of the level specified in the automation.

Details:

• Model: VTM31-SN (Thread/Matter)

• Mode: Dimmer Mode, Trailing Edge

• Switch Delay: Off

• Behavior:

  • Scheduled automations (e.g., “Set to 8% at 6:35 PM”) work correctly

  • Motion-triggered automations (“When motion detected, set to 2%”) instead turn the lights on to the previous brightness

  • Scenes do not resolve this

  • Default Level parameter does not affect automation behavior

Reproduction:

1. Set lights to 40%

2. Turn lights off

3. Trigger a HomeKit motion automation set to 2%

4. Lights turn on at 40% instead of 2%

Expected:
Motion automation should turn the lights on to the commanded brightness.

Actual:
Dimmer resumes last level and ignores the brightness value.