Chapter Output Template Losing Variables?

FM2017 / Win 7 / DITA 1.2

Setting up output templates for a DITA application.

Decided that I'd like to include the chapter title in my running header so that it would read "Chapter 1: Chapter Title"

So in my chapter output template, I edited one of the running header variables to accommodate. I believe it was Running H/F 5, which is already <$paratext[paratag]> and I filled in my chapter title style, which is head.0.

So basically, what I'm hoping to get is Chapter <$chapnum>: Running H/F 5 (<$paratext[head.0]>) (obviously, with the correct values in place of the building blocks).

I test with some content, it works in the template, I remove the content and save the template. For good measure, I made sure that I also updated the variable in the other templates I use for book building (Title, TOC, Index).

But now, when I output my map (book with FM components), what I get is Chapter <$chapnum>: with nothing further. I check the variable, and it has reverted to <$paratext[paratag]> without the specified paratag.

Why doesn't the variable definition stay with my template? I don't want to have to manually update it every time I output a book.