Hi-Res Production (available in ProSelect Pro) will split spreads into two parts if you have:

(a) Selected to "Split Doublespread Book Pages" in Preferences -> Hi-Res production -> Output Settings -> Output File

OR

(b) If you have used two single sided templates to make up your double spread book page.

In the later case, if you do not want the pages split, you can use "Join Book Pages" (under Album Menu) to combine pairs of single spread pages into double-spreads.