Windows with MenuBar have a larger minimum height to avoid artefacts (I fixed most of the vertical/horizontal artefacts, but the ones in rounded corners were too hard to fix).

imgui.cpp

@@ -4012,7 +4012,10 @@ static ImVec2 CalcSizeFullWithConstraint(ImGuiWindow* window, ImVec2 new_size)
         }
     }
     if (!(window->Flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_AlwaysAutoResize)))
+    {
         new_size = ImMax(new_size, g.Style.WindowMinSize);
+        new_size.y = ImMax(new_size.y, window->TitleBarHeight() + window->MenuBarHeight() + ImMax(0.0f, g.Style.WindowRounding - 1.0f)); // Reduce artifacts with very small windows
+    }
     return new_size;
 }