Is this a table view layout?
If it is, this is normal behavior for FileMaker if the user is adding/hiding columns or changing column width or location.
It wants to know if these changes should be saved so that the next users sees them or to keep them as a temporary change just for the current user's session.
This is a rather risky layout option for general users as they can accidentally get into trouble "losing" fields that have been resized too small and such. It's safer to set them up with a list view where they can't make such changes to the view in the first place.