引用 acmilan:
可能.NET的Text属性的实现有问题，建议尝试一下不改变Text属性，而是直接调用SetWindowText或者发送WM_SETTEXT设置文本。

// System.Windows.Forms.TextBox
public override string Text
{
    get
    {
        return base.Text;
    }
    set
    {
        base.Text = value;
        this.selectionSet = false;
    }
}

// System.Windows.Forms.Control
[Bindable(true), Localizable(true), DispId(-517), SRCategory("CatAppearance"), SRDescription("ControlTextDescr")]
public virtual string Text
{
    get
    {
        if (!this.CacheTextInternal)
        {
            return this.WindowText;
        }
        if (this.text != null)
        {
            return this.text;
        }
        return "";
    }
    set
    {
        if (value == null)
        {
            value = "";
        }
        if (value == this.Text)
        {
            return;
        }
        if (this.CacheTextInternal)
        {
            this.text = value;
        }
        this.WindowText = value;
        this.OnTextChanged(EventArgs.Empty);
        if (this.IsMnemonicsListenerAxSourced)
        {
            for (Control control = this; control != null; control = control.ParentInternal)
            {
                Control.ActiveXImpl activeXImpl = (Control.ActiveXImpl)control.Properties.GetObject(Control.PropActiveXImpl);
                if (activeXImpl != null)
                {
                    activeXImpl.UpdateAccelTable();
                    return;
                }
            }
        }
    }
}