Can you show a page, please? It’s difficult to diagnose CSS without being able to see the style sheet and markup.
If the elements in the list items were links and declared display:block that would cause vertical spacing to double in IE. Unlike most standards-based browsers, IE sometimes fails to collapse adjacent vertical margins in block elements.
But without seeing your site or page, it’s hard to tell. You could look to see if, inside the <li>
tags your content is inside yet another selector (spans? links?) or not. If that is the case, check any rules that apply to them to see if margin applies. If it does, comment that rule out, upload the style.css file, then retest in IE. If all is fixed (it’s like collapsed with no space) then adjust the padding of the <li>
tag, not the element within.
I run into this all the time with list-based navigation using wp_list_pages()
HTH