After testing some things in console I think (99% certain) this problem is be caused by you placing the the anchor href as '#.
You have a few options:
1) Replace the Anchor tags with something else. If you replace the the anchors with just P tags for example, and change your jquery to work off p.[class] rather than a.[class] it should fix the problem. (You can keep the same anchor styling by having cursor:pointer;
in your CSS to make it appear like a link when the mouse is over the link)
2) Prevent the default action of the link. Add return false
in your links eg <a class="work" href="#" onclick="return false;">Work</a>
The reason I think this may be the problem is because when you click an anchor that is "#" it will default take you to the top of the page, so I think it's taking you to the top of the page quickly, then returning and scrolling to the destination.