Use {{Box Blue|1====Some Heading===|2=* Some ** Stuff }}
ie. you are providing '===Some Heading===' as the parameter of name '1'. The presence of '=' on the value confuses the parser, so you need to tell it the name parameter name. It also fails with urls like www.example.org?id=1
Altenatively, you can use use {{Box Blue|<h3>Some Heading</h3>|* Some ** Stuff}} which doesn't use '='s