In kwin 5.12.0, all windows have a strange blue line between the top bar and the actual window content. See here: https://data.zx2c4.com/kwin-5.12.0-weird-blue-line.png https://data.zx2c4.com/kwin-5.12.0-weird-blue-line-settings.png This happens both with compositing and without. Here's an Xorg.0.log: https://א.cc/6etUMA9f
it's a new feature in plasma 5.12 and you can disable it. https://www.reddit.com/r/kde/comments/7r9ikm/how_do_i_remove_this_green_line_under_the_title/
Hi, thanks for reporting. It has always been there with breeze. What's new is that in the past it was automatically hidden when window and decoration background colors were identical. Now (because of some user's request), it is disabled via an option in the window decorations settings, disregarding the colors. Closing as "not a bug".