Intersection Type, properties not excluded from index signature

[cpamp]

TypeScript Version:
2.8.3

Search Terms:
intersection type index

Code

interface ExcludedIndex {
	excluded: number;
}

interface Index {
	[key: string]: string;
}

type Combined = ExcludedIndex & Index;

const obj: Combined = {
	anyString: "",
	excluded: 0
}

Expected behavior:
No Errors - should be able to assign excluded to obj.

Actual behavior:
Error:

[ts]
Type '{ anyString: string; excluded: number; }' is not assignable to type 'Combined'.
Type '{ anyString: string; excluded: number; }' is not assignable to type 'Index'.
Property 'excluded' is incompatible with index signature.
Type 'number' is not assignable to type 'string'.

Playground Link:
Link

Related Issues:
#24220 #23673 #20597

[mhegazy]

This the behavior of intersection types.

Duplicate of #17867