Anyhow, the thing concerns clicking on an interest on a userinfo page. Normally, you get the option to click a link to add that interest to your interests list, but if more than 2000 people have it you just get a message saying "There are [x] people and/or communities listing this as an interest. A list won't be shown."
What I thought would be convenient would be to still have the "If you're also interested in this and would like to be added to this list, click here." line appear to save having to fiddle about in the personal settings to add this interest just because more than 2000 people also have it. Anyway, I took a copy of interests.bml and added the line that says "if you're also interested..." to the end of the line that says "A list won't be shown". The modified file can be found here if anyone wants to see it.