Tab completion with argument completers

MyCompleter.ps1

# set up a test command
function Test-MyCompleter {
    param
    (
        [string[]]
        $Param1
    )
}

# register the completer
$ScriptBlock = {
    $List = 'aaaaaa','bbbbbb','cccccc'
    foreach ($Item in $List)
    {
        New-CompletionResult -CompletionText $Item -ToolTip $Item -ListItemText $Item -CompletionResultType ParameterValue
    }
}

TabExpansionPlusPlus\Register-ArgumentCompleter -CommandName Test-MyCompleter -ParameterName Param1 -ScriptBlock $ScriptBlock

# when I type this and press tab, completion should only offer 'bbbbbb'
Test-MyCompleter -Param1 b <TAB>

# however, it tab-completes through the list at the first index and I get
Test-MyCompleter -Param1 aaaaaa