Pages '09 v4.3 will advance to the next page when pasting images onto a page and there is insufficient room on the current page. Pages v5 (any release) will simply stack the pasted images above the last, and not advance to the next page. This is normal behavior for Pages v5 — whether you copy/paste, drag and drop, or use the Media selection from the Toolbar.
If you had Pages '09 v4.3 installed, it was silently moved into /Applications/iWork '09 folder after the Pages v5 installation. You can resume using Pages '09, and regain 100+ features over Pages v5.5.3. This will also restore your preferred image pasting behavior.
When it was initially released 20-months ago, Pages v5 was a complete rewrite, and inherited almost nothing from Pages '09, and has received scathing reviews from users that want a useful word processor again.