FocusManager.FocusedElement 无法让 NumericUpDown 聚焦

Describe the bug

使用 FocusManager.FocusedElement 没有办法让 NumericUpDown 一开始就聚焦

Steps to reproduce the bug

代码

 <Window
    x:Class="WpfApp6.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:hc="https://handyorg.github.io/handycontrol"
    xmlns:local="clr-namespace:WpfApp6"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="800"
    Height="450"
    FocusManager.FocusedElement="{Binding ElementName=Input}"
    mc:Ignorable="d">

    <Grid>
        <hc:NumericUpDown
            x:Name="Input" Focusable="True"
            Width="120"
            VerticalAlignment="Center" />
    </Grid>
 </Window>

Expected behavior

应该会在窗口打开时自动聚焦到文本框

Screenshots

No response

NuGet package version

HandyControl 3.5.1

IDE

Visual Studio 2022-preview

Framework type

.Net 9.0

Windows version

No response

Additional context

No response

Start with the provided Window XAML and the HandyControl NumericUpDown control, reproducing the issue on .NET 9 with HandyControl 3.5.1. Trace how FocusManager.FocusedElement interacts with the control during window startup. Done means the NumericUpDown receives focus automatically when the window opens, with the reported XAML scenario working as expected.