I was wrong, it's just actually bugged, just really bad UI. When you click the "Lightly wake me" button it disables the forms, but I didn't actually notice. So

I was wrong, it's just actually bugged, just really bad UI. When you click the "Lightly wake me" button it disables the forms, but I didn't actually notice. So I guess the time it didn't work for me I had clicked the button an even number of times, thus un-setting the alarm. Another nasty bit of UI - you can't use tab to move from hour to minute, minute to AM/PM, or AM/PM to the "Lightly wake me" button. Overall: a very simple and already-thought of idea, fairly badly implemented. Sorry to be so blunt, whoever created this.