Following gist https://gist.github.com/3002649, this fixes the leak following a MSFT suggestion but introduces event loss

repro-xmlschemaset-memoryleak-partly-fixed.ps1

function cleanup() {
	write-host "Cleaning up..."
	remove-item $schemaFile
	break
}

trap {
	cleanup
}

# The following was stolen from http://powershellquiz.com/post/10429186577/a4-one-bit-of-difference
Add-Type -Language CSharp -TypeDefinition @'
public class NullString {
    public override string ToString() {
        return null;
    }
}
'@
$null_for_dotnet_string = New-Object -TypeName NullString;


$TEST_SCHEMA = @'
<schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="urn:x">
	<element name="a" type="string"/>
	<element name="b" type="string"/>
	<element name="c" type="string"/>
	<element name="d" type="string"/>
	<element name="e" type="string"/>
	<element name="f" type="string"/>
	<element name="A" type="x:string"/>
	<element name="B" type="string"/>
	<element name="C" type="string"/>
	<element name="D" type="string"/>
	<element name="E" type="string"/>
	<element name="F" type="string"/>
</schema>
'@

$schemaFileName = [System.IO.Path]::GetTempFileName()

$TEST_SCHEMA > $schemaFileName

$count = 0

$N = 1000

1..$N |% {

	$schemaSet = new-object -typename System.Xml.Schema.XmlSchemaSet

	$xyzzy = register-objectevent -SourceIdentifier XYZZY $schemaSet ValidationEventHandler -MessageData $schemaFileName -Action {
		$a = $args[1]
		$e = $a.Exception
		$topLevelFileName = $event.MessageData
		$GLOBAL:count += 1
		write-host "#$GLOBAL:count $($topLevelFileName): $($a.Severity) in $($e.SourceUri) at line $($e.LineNumber) column $($e.LinePosition): $($e.Message)"
	}

	try {
		$reader = [System.Xml.XmlReader]::Create($schemaFileName)

		# Passing $null to a .NET method which expects a string
		# doesn't work: PowerShell passes an empty string instead,
		# which has a different (and incorrect) meaning for Add().
		[void] $schemaSet.Add($null_for_dotnet_string, $reader)

		# The following is an attempt to prevent events from getting lost,
		# based on a MSFT suggestion--but that doesn't work.
		while ($reader.Read()) {
		}

		$reader.Close()

		$schemaSet.Compile()
	} catch {
		write-host "$($schemaFileName): Exception: $_"
	}

	# The following works around a memory leak bug in the
	# PowerShell/.NET interaction.  But it introduces the
	# problem that validation events get lost.
	Unregister-Event XYZZY
	Remove-Job $xyzzy -Force
}

write-host