New-UDInput remains checked after reload

[adamdriscoll]

$page1 = New-UDPage -Name "Main" -Content {
New-UDInput -Title "MyTitle" -Endpoint {
param(
$userInput,
$inputType,
$UPNBox
)
    if ($inputType -eq 'login')
        {
        foreach ($value in $userInput)
            {
            try
                {
                $user = Get-ADUser -Identity $value -Server 'MyServer'
                }
            catch
                { 
                New-UDInputAction -Toast "Error" -Duration 1000
                }
            }
        if ($UPNBox) 
            {
            New-UDInputAction -Toast "Thanks" -Duration 500
            }
        }

        } -Content {
        New-UDInputField -Name 'inputType' -Type 'select'
        -Values @(
        "Login",
        "Username",
        "ComputerName")
        New-UDInputField -Name 'userInput' -Type 'textarea'
        New-UDInputField -Name 'SamAccountNameBox' -Type 'checkbox' -Placeholder 'SamAccountName'
        New-UDInputField -Name 'UPNBox' -Type 'checkbox' -Placeholder 'UPN'
    }
}

When $UPNBox is checked, the page will display the toast 'thanks', then the page will reload and the checkbox will appear unchecked
but if you click on submit again, the toast notification will be displayed again, even though $UPNBox 'should' be reset to false / unchecked