Either you can get a decent theme by somebody that know what they're doing with scripting
or if you want to tangle in it yourself
it's probably because there's a positioning script that goes off when you trigger the infinite scroll, you need to make sure that only goes off after all the images are loaded.
If you're site has masonry (multi-columned mosaicish layout) find the bit in the jquery a few lines after is says something like '$container.infinitescroll({'
it should say something like
function (newElems) {
$container.masonry( 'appended', $(newElems));
});
you need to change that middle line to
$(newElems).imagesLoaded(function() {$container.masonry('appended', $(newElems));});