I modified the homematic binding. This prevents openhab from auto updating the items if an error occures. In my case I have an instable connection to an outdoor device. Now I can see the right state in case of an error.
Feel free to check the pull request A fix to prevent item state updates if a homematic devices is not reachable. by csowada · Pull Request #3463 · openhab/openhab1-addons · GitHub.