# Create a cmdlet that has a [System.Collections.ArrayList] parameter.
Add-Type @'
using System;
using System.Collections;
using System.Management.Automation;

[Cmdlet(VerbsCommon.Get, "HashCode")]
public class AddCollectionItemCmdlet : Cmdlet
{
    [Parameter]
    public ArrayList Collection { get; set; }

    protected override void BeginProcessing()
    {
        WriteObject(Collection.GetHashCode());
    }
}
'@ -PassThru | % Assembly | Import-Module

# Use New-Object to create an array list.
# Note: Unlike when you use the static ::new() method, you get an instance
#       that is *wrapped in [psobject]*.
$al = New-Object System.Collections.ArrayList

$origHashCode = $al.GetHashCode()

# OK: Bypassing the [psobject] wrapper.
Get-HashCode -Collection $al.psobject.BaseObject | Should -Be $origHashCode

# !! BROKEN: Seemingly the array list is *cloned* if the input object
# !!         is [psobject]-wrapped.
Get-HashCode -Collection $al | Should -Be $origHashCode