このクソ仕様

SuperTrapOfPowerShellArray.ps1

function Fuga
{
    [OutputType([List[string]])]
    [CmdletBinding()]
    param()

    $array = [string[]]("a")
    return $array
}

(Fuga).GetType().FullName # System.String !?

SuperTrapOfPowerShellList.ps1

using namespace System.Collections.Generic;

function Hoge
{
    [OutputType([List[string]])]
    [CmdletBinding()]
    param()

    $list = New-Object List[string];
    $list.Add("a");
    return $list;
}

(Hoge).GetType().FullName # System.String !?