why does this error out?

[Cauterite via Digitalmars-d-learn]

Here's the output I get (DMD v2.068.2):

[1, 3, 10, 12, 21, 30, 100, 102, 111, 120, 201, 210]
core.exception.AssertError at std\range\package.d(4603): Assertion 
failure