Powershell: Odd behavior with dynamparam block

[LethiferousMoose]

Steps to reproduce

function Test-Function {
    [CmdletBinding(SupportsShouldProcess=$true, ConfirmImpact='Medium', DefaultParameterSetName='Set')]
    param([Parameter(Position=0)]
          [string] $Value,
          [Parameter(Position=1, ParameterSetName='Set')]
          [switch] $SetValue,
          [Parameter(Position=1, ParameterSetName='AnotherSet')]
          [switch] $AnotherSetValue,
          [Parameter(Position=2, ParameterSetName='Set')]
          [Parameter(ParameterSetName='AnotherSet')]
          [string] $BothSets)

    dynamicparam {
        if ($PSCmdlet.ParameterSetName -eq 'Set') {
            # Build parameter for Set
        }
        else {
            # Build parameter for AnotherSet
        }
    }

    process {
        Write-Output "Test"
    }
}

Expected behavior

$PSCmdlet.ParameterSetName to not reset back to it's default value when the parameter choosing the set has been provided.

Actual behavior

1. For Test-Function -Value 'Test':
   
   
   
   • $PSCmdlet.ParameterSetName equals Set (default parameter set, makes sense)
   
   
2. For Test-Function -Value 'Test' -AnotherSetValue 'SetParam':
   
   
   
   • $PSCmdlet.ParameterSetName equals AnotherSet (also makes sense because now we have a parameter provided that chooses a set that is not the default)
   
   
3. For Test-Function -Value 'Test' -AnotherSetValue 'SetParam' -BothSets 'BothSetsValue':
   
   
   
   • $PSCmdlet.ParameterSetName equals Set (I do not understand why this makes sense, we have provided AnotherSetValue in the provided parameters, why do I not see the chosen parameter set name being set?)
   
   

Note: the same behavior occurs even if BothSets does not have ParameterSetName defined.
Further note: I did other testing with trying to read the values of already provided parameters and it seems the dynamparam block only has visibility to the parameter currently in focus or being typed in the console.

Is this expected behavior, if so how can I build a dynamic parameter queuing off parameter data???

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      6.1.0-preview.2
PSEdition                      Core
GitCommitId                    v6.1.0-preview.2
OS                             Microsoft Windows 10.0.16299
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[BrucePay]

@LethiferousMoose The parameters returned by the dynamicparameter statement are actually _involved_ in determining the final active parameter set. You can't know which parameter set will ultimately be selected until all phases of parameter binding are done, up to and including binding from the pipeline if any parameters are so attributed. So you certainly can't rely on the parameter set being fixed when the dynamicparameters block is invoked.