A couple things I notice:
Clicking a new word doesn’t immediately add it to the Words tab, if the Words tab is currently open. You have to do something that forces a redisplay of the Words tab. Personally, my normal practice is to have the Words tab open and I click right in there to edit a new word that I think needs an immediate touch-up.
Then for the popover definition feature, it is very cool, but there are a few odd things:
If the sidebar is open and you have popover definitions showing, and then you close the sidebar, the popover definitions correctly reposition. But if you reopen the sidebar, the popovers do not reposition. (I don’t know what should happen if opening the sidebar causes some word to move to the next page, when its popover definition is currently showing.)
Also, the popover definitions render on top of the Edit Word dialog [and also the context list], if you open that up. It can make the dialog hard to use.
Third, an extremely minor thing, but the logic of where to display a popover relative to a multi-word phrase, which spans two lines, can result in the popover displaying in the middle of the page, near none of the words of the phrase. I don’t know if there’s an easy fix for that.