Declaring index signature based on property type gives invalid error

TypeScript Version: latest, demonstrable on playground (links below)

Search Terms: index signature diagnostics property type

Code:

interface BaseNode {
  kind: string;
  [key: string]: string | TokenNode["data"];
}

interface TokenNode extends BaseNode {
  kind: 'token';
  data: TokenData;
}

interface TokenData {
  offset: number;
  width: number;
  leading_width: number;
  trailing_width: number;
}

Expected behavior:

No errors, as the code is correct.

Actual behavior:

An error on interface TokenNode:

Interface 'TokenNode' incorrectly extends interface 'BaseNode'.
  Index signature is missing in type 'TokenNode'.

HOWEVER if I change TokenNode["data"] to its value TokenData, the error goes away.

Playground Link:

Code above displaying the error
Code above with the fix, no errors

Reproduce both linked TypeScript Playground examples, comparing the indexed-access form with the equivalent TokenData form. Trace the type-checking behavior for the BaseNode and TokenNode interface declarations; done means the indexed-access version no longer reports the invalid inheritance error while the existing valid case remains error-free.