Write-Debug ignores Debug switch in Foreach-Object Parallel block

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

Run this script with two identical blocks of code except for the "Parallel" option.

Write-Host 'Test 1 - non-parallel'
$DebugPreference = 'SilentlyContinue'
1..2 |
ForEach-Object {
    Write-Debug "Item $_`: Write-Debug" 
    Write-Debug "Item $_`: Write-Debug -Debug" -Debug 
    Write-Debug "Item $_`: Write-Debug -Debug:`$true" -Debug:$true 
    Write-Debug "Item $_`: Write-Debug -Debug:`$false" -Debug:$false 
} 

Write-Host 'Test 2 - parallel'
$DebugPreference = 'SilentlyContinue'
1..2 |
ForEach-Object -Parallel {
    Write-Debug "Item $_`: Write-Debug"
    Write-Debug "Item $_`: Write-Debug -Debug" -Debug
    Write-Debug "Item $_`: Write-Debug -Debug:`$true" -Debug:$true
    Write-Debug "Item $_`: Write-Debug -Debug:`$false" -Debug:$false
}

Write-Host 'Done'

Expected behavior

Test 1 - non-parallel
DEBUG: Item 1: Write-Debug -Debug
DEBUG: Item 1: Write-Debug -Debug:$true
DEBUG: Item 2: Write-Debug -Debug
DEBUG: Item 2: Write-Debug -Debug:$true
Test 2 - parallel
DEBUG: Item 1: Write-Debug -Debug
DEBUG: Item 1: Write-Debug -Debug:$true
DEBUG: Item 2: Write-Debug -Debug
DEBUG: Item 2: Write-Debug -Debug:$true
Done

Actual behavior

Test 1 - non-parallel
DEBUG: Item 1: Write-Debug -Debug
DEBUG: Item 1: Write-Debug -Debug:$true
DEBUG: Item 2: Write-Debug -Debug
DEBUG: Item 2: Write-Debug -Debug:$true
Test 2 - parallel
Done

Error details

NA

Environment data

Name                           Value
----                           -----
PSVersion                      7.4.3
PSEdition                      Core
GitCommitId                    7.4.3
OS                             Microsoft Windows 10.0.19045
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

Start by running the provided reproduction script and compare Write-Debug behavior in ordinary and ForEach-Object -Parallel blocks. Trace the ForEach-Object -Parallel and Write-Debug entry points to determine why the Debug switch is ignored, then verify that the parallel block produces the expected debug lines while respecting DebugPreference.