As you probably noticed, Microsoft got rid of those ridiculous fat borders around the windows. At last! Now the borders in Windos X are nice and 1-pixel thin. Unfortunately, Reaper does not follow the trend but makes its own - we have three (3) kind of borders for plugin windows: conventional 1px border at the top, two white borders at the right and at the bottom, one transparent border at the left. Thank you very much :\
Moreover, some windows have only the top border, such as Mixer or Item Properties, and some have top and bottom, such as Routing/Group/Render Matrix. Why the hell the visual component of the Reaper is always in the arse? By the way, I'm 100% sure that this little nitpick (as well as tons of other ones) will never ever be fixed.