Extra flow

Hi there, since a few months ago I've a problem with Framemaker 12.

When I'm formatting a book another flow apears at the end of the book.

The second flow has the same Tag and I only can get rid of it by deleting the pages.

Normaly a save makes the book page even and deletes al the empty pages in the back.

When I have the second flow it won't work like that.

Today I'm formatting a book and when I choose a none-masterpage for a page there's a second flow appearing in the middle of my book.

How does this happen, why does this happen? Hopefully you have an answer for me. Thanks in advance.