User blog comment:DaNASCAT/Going Up To Speed On Wikia's Performance Initiative/@comment-452-20131107230844/@comment-11733175-20131108002208

That's likely because the blog comments are loaded when they come into view rather than as soon as possible for the sidebar. I would imagine it doesn't attach event listeners until the sidebar is loaded (or the listeners are added after the sidebar loading completes in terms of where the script is located in the loading order).

One fix is to use CSS's :hover pseudo-class which I suggested through ComSup a number of months ago. I believe you can add it in yourself although it may take a few bits of trial and error before it works all the time.