This is referring to the little popup windows showing you the individual notes and references at the bottom of a page. They work fine with zoom at 100% but break at other zoom levels (have tested 90%, 110%, 125%) as I will show. Mainly tested in Chrome (windows and mac) but I have also tested and seen it in Firefox and Safari as well.

Here is what the popup should look like:

Here is what it looks like when it breaks. It's in the completely wrong spot (other side of the window). Sometimes it will work the first time and then break like this if you hover over it again.

Sometimes it also looks like this. The box is in the correct spot but the triangle/arrow is displaced.

This also affects Chrome's new smart zoom at regular zoom level. The popup is just entirely displaced in that case. Doesn't seem to affect Safari though so that may be an issue in the browser's implementation?

I searched around and couldn't find anything, which is surprising because personally I find the default font size to be too small on my mac so I run into this bug all the time.