Appendix in Word document is being subordinated to a heading

I have formatted an appendix using Word's built-in formats but for some reason the appendix is being subordinated to the regular headings. So, for example, if I trying to insert a cross reference, I get this:

In this case the Appendix A should be at the top level, not subordinated to Section 11.

I tried adding a section break, but that made no difference, it only changed the page numbers. How can I get the Appendix to the top level?