asp.net自定义控件呈现在表单标记之外

I am having an issue with a custom control rendering its contents (child controls) outside of the tag which leads to runtime errors and issues. In an attempt to simplify things as much as I can, I created the control below but it has the very same issue. I have tried inheriting from Control, WebControl and CompositeControl all resulting in with the same problem. Guessing there is something obvious that I am doing wrong... Thanks for any help.I am having an issue with a custom control rend