file IO, is this a bug in Powershell?

When using the New-Object cmdlet and the target type constructor takes in parameters, you should either use the -ArgumentList parameter (of New-Object) or wrap the parameters in parenthesis - I prefer to wrap my constructors with parens:

# setup some convenience variables to keep each line shorter
$path = [System.IO.Path]::Combine($Env:TEMP,"Temp.txt")
$mode = [System.IO.FileMode]::Append
$access = [System.IO.FileAccess]::Write
$sharing = [IO.FileShare]::Read

# create the FileStream and StreamWriter objects
$fs = New-Object IO.FileStream($path, $mode, $access, $sharing)
$sw = New-Object System.IO.StreamWriter($fs)

# write something and remember to call to Dispose to clean up the resources
$sw.WriteLine("Hello, PowerShell!")
$sw.Dispose()
$fs.Dispose()

New-Object cmdlet online help: http://go.microsoft.com/fwlink/?LinkID=113355

Another way would be to use just the name of the value and let PowerShell cast it to the target type:

New-Object IO.FileStream $filePath ,'Append','Write','Read'