To reproduce: change to 150% DPI scaling and try to show a RadDesktopAlert. 

Workaround:

        bool isFirstTime = true;

        private void radButton1_Click(object sender, EventArgs e)
        {
            this.radDesktopAlert1.CaptionText = "New E-mail Notification";
            this.radDesktopAlert1.ContentText = "Hello Jack, I am writing to inform you " +
                                                "that the planning meeting scheduled for Wednesday has been postponed and" +
                                                "it will eventually be rescheduled, possibly for the next Tuesday";
            if (isFirstTime)
            {
                this.radDesktopAlert1.PopupAnimation = false;
                this.radDesktopAlert1.Show();
                this.radDesktopAlert1.Hide();
                this.radDesktopAlert1.Show(); 
                isFirstTime = false;
            }
            else
            { 
                this.radDesktopAlert1.Show();
            }
           
        }