Did a quick test without the plugin installed, if a rebuild is running at the time scheduled for a parity check it will attempt to start one but since the rebuild is already running nothing happens, on the other hand if the rebuild is paused, I did it manually but it would be the same if paused by the plugin, then it re-starts the current rebuild from the beginning, so it's an Unraid bug, it's a minor one and one that won't affect many users but it might still be worth reporting.