How do I undo a Task I accidentally deleted or find it in a Trash somewhere?? I now don't know what it was I had to do!

I've just started using Tasks and thought that checking the checkbox would make my command to delete apply to that Task. It doesn't. It deletes the task that is grey-selected, not the one that is checkbox-selected. So I deleted some task at the bottom of my list and I don't know what it was. How do I get it back please? Ctl-Z does not seem to do anything and I can't find Undo or even a Trash anywhere...