Keep Option spreads out previous lines

I have a book where each chapter heading follows the previous para after a space. I want each chapter heading to start on a new page so I go to the 'chapter heading' para style keep option and choose 'Start para on next odd page' and it does. However, the para lines on the previous page (with what I have named the 'standard para' style) spread out vertically so they fill the page.. How do I stop that happening? It must be simple but have tried every permutation I can think of with no success.