repro2.ps1

workflow repro2
{
    $ErrorActionPreference = 'Stop'
    $dir = 'whatever'
    InlineScript
    {
        $d = $using:dir
        if ($d -eq $null) { throw "!!!!! BUG: d is null" } else { "d is $d" }
    }

    InlineScript
    {
        Get-Date
    }

    InlineScript
    {
        $d = $using:dir
        if ($d -eq $null) { throw "!!!!! BUG: d is null" } else { "d is $d" }
    }
}

Reproduce-InlineScriptUsingBug.ps1

[CmdletBinding()]
Param (
	[Parameter(Mandatory = $true)]
	$targetComputer
)

workflow repro
{
	Param (
		[string] $EAP = 'Stop'
	)
	$ErrorActionPreference = $EAP

	Write-Output "${Env:ComputerName} before InlineScript #1: dir is $dir"
	InlineScript {
		Write-Output "${Env:ComputerName} inside InlineScript #1: dir is $using:dir"
		'Get-Date' | Set-Content C:\ExistingScript.ps1
	}

	$dir = 'C:\Program Files (x86)\Contoso App'
	Write-Output $dir

	Write-Output "${Env:ComputerName} before InlineScript #2: dir is $dir"
	InlineScript {
		Write-Output "${Env:ComputerName} inside InlineScript #2: dir is $using:dir"
		if ($using:dir -eq $null) { throw "!!!!! BUG: dir is null" } else { Write-Output "----- ok: dir is not null" }
	}
	Write-Output "${Env:ComputerName} before InlineScript #3: dir is $dir"
	InlineScript {
		# referencing $using:dir prevents the bug
		#Write-Output "inside InlineScript #3: dir is $using:dir"
		# creating the file inside this InlineScript prevents the bug
		#'Get-Date' | Set-Content C:\ExistingScript.ps1
		# writing anything to output before external script invocation prevents the bug
		#Write-Output 'dummy'
		# executing a trivial statement with no output before external script invocation prevents the bug
		#$a = 1

		# variant 1: invoking an existing external script TRIGGERS the bug
		& C:\ExistingScript.ps1
		
		# variant 2: invoking a nonexistent external script TRIGGERS the bug (observable upon next workflow invocation)
		#& C:\NonExistentScript.ps1

		# variant 3: throwing an exception instead of invoking a script DOES NOT trigger the bug
		#throw 'Boom!'

		# writing anything to output after external script invocation prevents the bug
		#Write-Output 'dummy'
		# writing anything to verbose after external script invocation prevents the bug
		#Write-Verbose 'bla'
		# executing a trivial statement with no output after external script invocation prevents the bug
		#$a = 1
	}
	
	Write-Output "${Env:ComputerName} before InlineScript #4: dir is $dir"
	InlineScript {
		Write-Output "${Env:ComputerName} inside InlineScript #4: dir is $using:dir"
		if ($using:dir -eq $null) { throw "!!!!! BUG: dir is null" } else { Write-Output "----- ok: dir is not null" }
	}
}

Write-Host "===== Restarting WinRM on $targetComputer ====="
icm $targetComputer { Restart-Service WinRM } -ErrorAction SilentlyContinue
Start-Sleep -Seconds 2

Write-Host '=========== Scenario 1: BUG if ErrorActionPreference is Stop ==========='
Write-Host '===== Step 1a ====='
repro -PSComputerName $targetComputer -EAP 'Stop'
Write-Host '===== Step 1b ====='
repro -PSComputerName $targetComputer -EAP 'Stop'

Write-Host "===== Restarting WinRM on $targetComputer ====="
icm $targetComputer { Restart-Service WinRM } -ErrorAction SilentlyContinue
Start-Sleep -Seconds 2

Write-Host '===== Step 1c ====='
repro -PSComputerName $targetComputer -EAP 'Stop'

Write-Host "===== Restarting WinRM on $targetComputer ====="
icm $targetComputer { Restart-Service WinRM } -ErrorAction SilentlyContinue
Start-Sleep -Seconds 2

Write-Host '=========== Scenario 2: ok if ErrorActionPreference is Continue ==========='
Write-Host '===== Step 2a ====='
repro -PSComputerName $targetComputer -EAP 'Continue'
Write-Host '===== Step 2b ====='
repro -PSComputerName $targetComputer -EAP 'Continue'

Write-Host "===== Cleaning up ====="
icm $targetComputer { if (Test-Path C:\ExistingScript.ps1) { Remove-Item C:\ExistingScript.ps1 } }