Select Smart Text Reflow.
Preserve Facing-Page Spreads: This option determines whether facing-page spreads are preserved when text is reflowed in the middle of a document. If this option is selected when text reflows in the middle of the document, a new two-page spread is added. If this option is not selected, a single new page is added, and subsequent pages are "shuffled."
If your layout includes design elements specific to the right or left side of the spread, turn on this option. If your left and right pages are interchangeable, you can turn off this option. This option is dimmed if the document does not have facing pages.