I have never had a problem with these type of caps poping off. It does sometimes get too hot if my recipe included clay or milk, and you can see wet spots of condensation forming.
Candlewic has one as well, its in their ultimate fragrance section Mango Mandarin BBW Type A vibrant summertime blend of juicy sweet mango and sparkling mandarin, topped off with cool dewy green notes. A BBW favorite!