Disallowing widows in InDesign causes breaks in the middle of the page

When using Keep Options to disallow widows in InDesign, paragraphs will randomly break in the middle of pages. I've been following the correct instructions for disallowing widows—keeping lines together at the start and end of paragraphs with 1 line at the start and 2 at the end (I’ve also tried this with 2 lines at the start, but that doesn’t help the issue). When the breaks fall in the middle of pages, there’s nothing that I can do to fix it. I’ve tried adding a return after the broken paragraph to see if that will help it to move to the correct page, but it doesn’t work. I’ve also tried lengthening and shortening the text box, and that doesn’t work either. 

Also, weirdly, this only happens with some documents, not all. Is this a glitch, and if so, what can be done to fix it?