Customize the header on a .action/.ftl page

In PS7 we have customized the wildcards for our headers in PowerTeacher (teachers_header_css.txt and teachers_header_fr_css.txt).

Those changes are not showing up, however, on any PowerTeacher pages that use a .ftl file (for example, teachers/attendance-grid.action). It seems to be using the original wildcard and completely ignoring my customization.

I'm even more confused by the attendance-grid.ftl file because I can't see where it is even rendering the html for the header (for example, the PowerTeacher logo at the top of the page). It seems to be injecting the html code magically into the page without any markup or code telling it to do so.

How can I get this page to display my customized header?

Any ideas?