Here's how I'm trying to do this, but I find it includes items that are checked out to "tcm:0-0-0" as well as my user ID.
$filter = New-Object Tridion.ContentManager.CoreService.Client.RepositoryLocalObjectsFilterData;
$lockUserLink = New-Object Tridion.ContentManager.CoreService.Client.LinkToUserData
$lockUserLink.IdRef = $UserId
$filter.LockUser = $lockUserLink
$client.GetSystemWideList($filter)
Is this a defect in my code or a product defect (or an undocumented feature)?