css html 5 menu shifts left on some pages

I cannot figure out why, but on certain pages like:

http://www.serif.cz/folio.htm

the menu shifts just a bit to the left of where it appears on the rest of the site:

http://www.serif.cz/

I have compared the HTML and it looks exactly the same.

Any ideas?

Its the scroll bars. Firefox and Chrome do not display scroll bars unless the content actually needs to scroll. IE will display a disabled scroll bar if the content does not scroll.

You can add a disabled scroll bar to pages that do not have content long enough for a scroll by using the following CSS:

body{overflow-y:scroll;}

Or you can just kind of accept the fact that it's going to do it on those pages. It's just one of those things where it makes sense why it's happening, it's just annoying. :)