Restriction on type not applying when used within a mapping

[aka-mj]

I have the following

typealias Lang = String(matches(Regex(#"^[a-z]{2}$"#)))

m = new Mapping<String, Lang> {
	["0"] = "en"
	["1"] = "de"
	["2"] = "fr"
	["3"] = "e"
}

I'd expect an error because line ["3"] = "e" value doesn't match the regex for type Lang, but pkl produces the following:

{
  "m": {
    "0": "en",
    "1": "de",
    "2": "fr",
    "3": "e"
  }
}

[translatenix]

It's a known issue.
Mapping entries are only type-checked if the mapping is assigned to a typed property:

m: Mapping<String, Lang> = new {...}

The same holds for listing elements.