Rule to postUpdate an Item works but Item falls back after some seconds

Thats it. I misunderstood the autoupdate function. Thanks for your detailed answer. That helped me solving it:
The setup in the house is:

  • Hardware push buttons
  • Tinkerforge (Industrial Digital Out)
    -> both are connected to a relay and work on the same voltage level. The relay has two potential-free outputs. One for the light itself and one connected to tinkerforge to monitor the state (IO-16)

The OH setup is now very similar to yours:
Items:

  • Proxy_light_switch with no binding (on sitemap to provide light state and ON-OFF-function)
  • Light_switch with binding to tinkerforge (Industrial Digital Out) switch which itself switches the hardware relay/light on. (Due to the hardware relay which expects a push (on-off) a rule sends command off when on was received.)
  • Contact bound to IO-16 tinkerforge module that monitors the state of the relay.

Rules:

  • Contact switch checks for change from open to closed and vice versa and posts the update to the proxy_light_switch. This brings the Proxy_light_switch always to the correct status, independent if the hardware push button was used or the OH push button. No command, just update.

  • The proxy switch is monitored by a rule. The rule checks first the status of the light, if its different from the received command, the light_switch (with push button rule) is triggered with a real command.
    In case OH is used to switch the light on or off the proxy is “double updated”. Because the contact switch posts the update of the relay to the Proxy_light_switch as well.

-> Solved!