For text variables for running headers/footers, the default behavior is as described in the help: "If there is no occurrence of the style on the page, the previous occurrence of the applied style is used." Not sure if this is a bug or a feature, but if you are using headers or footers for both sections and subsections, and some sections have subsections and some don't, then you get a header with the name of a subsection many pages back, even though it's not on the page. Having an option to turn off this persistence would make this feature work much better. I've finally had to give up on subsection headers as they just don't work.