Inconvenient AnonymousPermMask64

AnonymousPermMask64Test.ps1

$web = get-spweb $url
$list = $web.Lists["Documents"]

# get ready for some sneaky backdoor business
$flags=[Reflection.BindingFlags] "NonPublic,Instance"
$arr  =[Microsoft.SharePoint.SPList].GetField("m_arrListProps", $flags).GetValue($list)
$i    =[Microsoft.SharePoint.SPList].GetField("m_iRow", $flags).GetValue($list)

# make sure we're going to set some new value
$newMask = $null
$oldMask = $list.AnonymousPermMask64 
if ( $oldMask -eq "BrowseUserInfo" ) {
    $newMask = [Microsoft.SharePoint.SPBasePermissions]::OpenItems
}
else {
    $newMask = [Microsoft.SharePoint.SPBasePermissions]::BrowseUserInfo
}

function Dump([string]$msg) {
    Write-Host "========== $msg"
    Write-Host "Value     " $list.AnonymousPermMask64
    Write-Host "IsNull    " ($list.AnonymousPermMask64 -eq $null)
    Write-Host "RawValue  " $arr.Get(21,$i)
    Write-Host "RawType   " $arr.Get(21,$i).GetType()
    Write-Host "RawAsLong " ([long] $arr.Get(21,$i))
    Write-Host "RawAsSPBP " ([Microsoft.SharePoint.SPBasePermissions]([long]$arr.Get(21,$i)))
}

Dump "Initial"

$list.AnonymousPermMask64 = $newMask
Dump "Set new value $($newMask)"

$list.Update()
Dump "SPList.Update()"

$arr.Set(21,$i,[long]$oldMask)
Dump "Raw set cast new value $([long]$oldMask) ($oldMask)"
$list.AnonymousPermMask64 = $newMask # cleapup (raw-set leaves in consistent state)
$list.Update()

$list.AnonymousPermMask64 = $oldMask
$web = Get-SPWeb $web.Url
$list = $web.Lists[$list.ID]
Dump "Set ($oldMask), reload web/list without Update()"

<#
========== Initial
Value      BrowseUserInfo
IsNull     False
RawValue   134217728
RawType    System.Int64
RawAsLong  134217728
RawAsSPBP  BrowseUserInfo
========== Set new value OpenItems
Value     
IsNull     True
RawValue   OpenItems
RawType    Microsoft.SharePoint.SPBasePermissions
RawAsLong  32
RawAsSPBP  OpenItems
========== SPList.Update()
Value      OpenItems
IsNull     False
RawValue   32
RawType    System.Int64
RawAsLong  32
RawAsSPBP  OpenItems
========== Raw set cast new value 134217728 (BrowseUserInfo)
Value      BrowseUserInfo
IsNull     False
RawValue   134217728
RawType    System.Int64
RawAsLong  134217728
RawAsSPBP  BrowseUserInfo
========== Set (BrowseUserInfo), reload web/list without Update()
Value      BrowseUserInfo
IsNull     False
RawValue   BrowseUserInfo
RawType    Microsoft.SharePoint.SPBasePermissions
RawAsLong  134217728
RawAsSPBP  BrowseUserInfo
#>