Weird spacing issue with running footer

I have the same running footer on the same master applied to every recto page of this document. It includes this variable text:

It works like a charm throughout, except on the first page of each lesson, where it adds an extra space *within the variable text itself*!

So on a regular page, it looks like this:

But on the first page of the lesson, it looks like this:

Every single lesson that starts on a recto is the same. It's obviously pulling from the same text to create the variable, the only difference being that these are the pages where that text first appears. What strange dark magic is causing this?

And here's the top of the page whence it's pulling the text:

I'm on Windows with, I believe, the latest update of CC:

Thanks.

~Valerie