Type cast is not highlighted in hash table

[lastsecondsave]

$Config = [PSCustomObject] @{
    Key = [String]10
    Group1 = [PSCustomObject] @{
        Key1 = ''
        Key2 = ''
    }
    Group2 = [PSCustomObject] @{
        Key1 = ''
        Key2 = ''
    }
}

String and PSCustomObject in second and third line are not highlighted. Every other type cast is highlighted.