After looking everywhere and even doing a fresh install I took a look at you r demo page and it seems to do the same thing.
When you first load the site and click on one of the links to scroll down the page to say ‘Services’ it will scroll down the one page just past the title of the section. (See image)
If you click the ‘Services’ button again then it will correct its self and scroll up just slightly where you can then see the title of the section. (See image)
This was capped from the demo you have and it seems that it happens on my current install as well as the other fresh installs I did. I have tried to find what might cause i but I am at a loss.
Please let me know if there is anything that might help you discover this.
Also I tried posting earlier and I don’t know if it really posted, my connection failed out. Sorry if this is a double post.