Formatting removed from VariableDeclaration when changing it's kind

When running the following program:

``` js
var recast = require('recast');
var ast = recast.parse(
'var a = 1,\n' +
' b = 2,\n' +
' c = 3;'
);
ast.program.body[0].kind = 'let';
console.log(recast.print(ast).code);
```

I would expect this output:

``` js
let a = 1,
b = 2,
c = 3;
```

But instead I get:

``` js
let a = 1, b = 2, c = 3;
```

Somehow changing the `kind` of a VariableDeclaration removes all the indentation.

However, when I change `declarations` of VariableDeclaration in all kinds of ways (without changing the number of items), the formatting is preserved correctly.

Interestingly when I add a comment between the declarations, and then change the `kind`, the formatting is preserved.

Run the provided recast.parse and recast.print reproduction, then trace how a VariableDeclaration is printed after its kind changes. Compare that path with changing declarations and with the commented example; done means changing var to let preserves the original line breaks and indentation.

Written by the indexing model from the issue text.