When adding headers/footers, a stroke is added to body text

I have a PDF version 1.6 that I'm opening in Acrobat Pro X. When I add headers/footers, some of the text (not all, and not on all pages) gets a stroke added to it, making it much bolder than it originally was. In this PDF, there are some text elements that have a stoke already - intentionally - but adding the header/footer applies the stoke to text that is not intended to have a stoke. How can I prevent this?