I'm trying to add a new field to a SharePoint list and set its internal name. I have both the static name and display name specified but I can't figure out why the internal name gets set as First_x0020_Name.
$web = Get-SPWeb 'https://server'
$list = $web.Lists['listName']
$newFieldXML = '<Field Type="Text" StaticName="FirstName" DisplayName="First Name"></Field>'
$list.Fields.AddFieldAsXml($newFieldXML)