-ListAvailable:$false not respected in Get-TimeZone #26462

Prerequisites

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• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

This is a sub-issue of #25242.

The cmdlet Get-TimeZone does not respect explicit $false values for the -ListAvailable switch parameter.

PS> $result = Get-TimeZone -ListAvailable:$false
PS> $result.Count
PS> $result.Id

Expected behavior

PS> $result = Get-TimeZone -ListAvailable:$false
PS> $result.Count
1
PS> $result.Id
Tokyo Standard Time

-ListAvailable:$false should behave the same as omitting the -ListAvailable switch, returning only the current time zone.

Actual behavior

PS> $result = Get-TimeZone -ListAvailable:$false
PS> $result.Count
142
PS> $result.Id
Dateline Standard Time
UTC-11
Aleutian Standard Time
Hawaiian Standard Time
Marquesas Standard Time
...

-ListAvailable:$false behaves the same as -ListAvailable or -ListAvailable:$true, returning all available time zones.

Error details

No error is thrown. The cmdlet executes but ignores the explicit $false value.

Environment data

PS> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.5.4
PSEdition                      Core
GitCommitId                    7.5.4
OS                             Microsoft Windows 10.0.26100
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response