Very strange issue. We've coded internal page links (e.g. href="#content") with top links (e.g. href="#top") to navigate back and forth on an FAQ page. Typical stuff.
Problem is, as soon as one of the internal links is clicked, the topmost part of the page loses about 4px, so the 7px border at the top of the header becomes 3px. And this is also throwing drop down menus off about 4px so they are unusable.
In 10 years of web development, I've never come across this issue.
The page in question is found here: