The CalDAV-personal binding has a bug: It does not reliably enable assiociated switches.
This has been fixed. If you use the binding and would like to support the developers, please visit this thread CalDAV personal: Switch item ON only during server reload, but on time for OFF or directly go to GitHub ([CalDAV-personal] Switch item ON only during server reload, but on time for OFF · Issue #5744 · openhab/openhab1-addons · GitHub) to download the JAR files. Please enable debug login for CalDAV and post your log files…
Thanks!