Spurious 'multiple schemas match' warning?

[ariane-emory]

I have set the following simple configuration for the extension:

  "prettifySymbolsMode.substitutions": [
    {
      "language": "rust",
      "substitutions": [
        {
          "ugly": "fn",
          "pretty": "λ",
          "style": {
            "color": "#8d8"
          }
        }
      ]
    }
  ]

Functionally, this configuration appears to work as intended, but it result in a "Matches multiple schemas when only one must validate." warning. How can I resolve the issue?