An issue we recently experienced with our SharePoint 2010 document sharing site had to do with List Item ECB Context Menu hover positioning on large document libraries that required you to scroll down to see all items. When you hover over a list item, the expected behavior is that the context menu would be displayed to the right of the document title, and this is the case for the most part, until you have to scroll down to see a document. Then when you hover over the item, the context menu appears farther up in the library, as depicted in the following example:
Not pretty. 
Upon further research, I discovered that this had to do with the fact that SharePoint 2010 attempts to override default browser scrolling. By reading the following blog article by Kyle Schaeffer, I was able to override SharePoint 2010’s default scrolling behavior, which in turn fixed the above SharePoint list item context menu positioning issue.
Thank you, Kyle!