Epub sample pagination problem

Hello,

the problem is next - the books was published to itunes, but when i've upload the sample file all page-breaks doesn't seems to work(in full book, that i've also download from store, everything is fine). I provide a custom sample when upload book with Itunes Producer. Before uploadin i've check the sample with Book Proofer and it was fine. For pagination i'm using page-break-before: always, css is in external file.

Is it possible to fix it without cutting it to separate files in the sample?