Is this a bug? What's the deal?

EnumBug.ps1

# Add an enum with All constant
Add-Type -TypeDefinition @'
    using System;

    [Flags]
    public enum O365Services
    {
        AzureActiveDirectory,
        Exchange,
        Sharepoint,
        Skype,
        All = AzureActiveDirectory | Exchange | Skype | Sharepoint
    }
'@

# Enumerations work as expected
PS c:\> [O365Services]::AzureActiveDirectory
AzureActiveDirectory

PS c:\> [O365Services]::Exchange
Exchange

PS c:\> [O365Services]::Sharepoint
Sharepoint

# Except for whatever is the 4th value
PS c:\> [O365Services]::Skype
All