Master page text frames and new pages

Hi folks,

I don't even know the terminology here for what I'm trying to find the answer to so I've been having trouble coming up for a solution for this.

I have a large document that has a two-column master text frame on each page and a series of auto-flowed text through them. There is a thick border on the outside edges of each page, so the position of the text frame is placed more towards the spine on each page - meaning it's not in the same spot on opposing pages, not centred, whatever you'd like to say about it.

Here's the issue - when the client decides they simply must add an odd-number of pages to the inside of the book somewhere, those text frames don't move position towards the spine, even though they are placed there on the master. I'm not sure if I explained that well enough. But say I've got a page on the lefthand side, the border is on the outside edge of the page, so the text frame is towards the righthand side of the page. Now I have to add a page before that one, so what results is my page is now on the righthand side of the book, it now has the border on the righthand side of the page, and the text box is also still towards the righthand side of the page as well. It doesn't automatically move over to the left even though the master sort of tells it that's where it should be. Is there a way around this?

Thanks!
-Andy