Another great example is CSD (client-side decorations). Classic X window managers do not handle them well, and many users do not want them, but they were added

Another great example is CSD (client-side decorations). Classic X window managers do not handle them well, and many users do not want them, but they were added in GTK+ 3.10 with no reasonable way for the window manager to disable them. Basically breaking all environments besides Gnome. Thus work-arounds like https://github.com/PCMan/gtk3-nocsd https://github.com/PCMan/gtk3-nocsd