Why does casting PSCustomObjects to custom type with DateTime in PowerShell fails?

Question

I would like to cast PSCustomObjects to custom types. Casting does work for simple types, but it doesn't work if I use e.g. DateTime within the type definition. Casting from a HashTable to custom type does work. Why does casting from PSCustomObject does not work as expected?

Here's an example:

Add-Type @"
using System;
public struct Test {
    public DateTime date;
}
"@

$Properties = @{date=(Get-Date)}
$CustomObject = New-Object -TypeName PSCustomObject -Property $Properties

# Returns correct date:
$TestObjectCastFromProperties = [Test]$Properties
$TestObjectCastFromProperties
$TestObjectCastFromProperties.GetType()

# Returns wrong date
$TestObjectCastFromCustomObject = [Test]$CustomObject
$TestObjectCastFromCustomObject
$TestObjectCastFromCustomObject.GetType()

Answer 1

I can't tell you why this doesn't work. Even the explicit conversion fails:

[System.Management.Automation.LanguagePrimitives]::ConvertPSObjectToType(
    $CustomObject, [test], $true, [cultureinfo]::InvariantCulture, $false)

Output:

date               
----               
01.01.0001 00:00:00

---

However, you could use a handcrafted function to convert a PSCustomObject to a Type:

function Cast-CustomObject
{
    Param
    (
        [PsCustomObject]$obj,
        [Type]$castType
    )
    $properties = ($obj.PSObject.Properties | % { @{$_.Name = $_.Value}})
    [System.Management.Automation.LanguagePrimitives]::ConvertTo($properties, $castType)
}

Usage:

Cast-CustomObject -obj $CustomObject -castType ([Test])

Output:

date               
----               
06.07.2016 08:52:01