Zooming is un-docking my document

Hello ,

W7, Framemaker 11.

I work with a book, and all the files from that book, open. The files from the book are all consolidated.

Recently when I zoom in or out, Framemaker un-docks the file. If I carry on zooming, the  file underneath the active file  responds.

I then have to move the file and then in a seperate movement, re-dock.

It really is surprising how annoying this is.

Any ideas?