I've recently reset the thumb frame spacing in my current theme and find changing from 3px to 10px the thumbs don't all always load. It's intermittent, but seems to happen more often than not.
My "Gallery One" (see the www link below for the gallery), has 14 images, shows 14 images in the page count, but only actually displays 12 images with no page button.
Likewise, "Gallery Two" has 17 images but only displays 13 (with the page button showing).
It's the same in Safari on Mac, and Chrome & IE on Windows XP. With the exception in Safari that if I resize the browser and reload it will sometimes show all the thumbs.
If I change the spacing back to 3px, everything displays correctly in all browsers again. I'll leave it @ 10px until ya'll get a chance to see it -;)