Fix sectionless files silently dropping all settings

Src/ConfigurationReader.cs

@@ -107,6 +107,14 @@ private static void Parse(StringReader reader, Configuration config)
           currentSection.Add(setting);
         }
       }
+
+      // If the source contained settings but never opened a named section, the
+      // default section was never added above (that only happens when the first
+      // '[' is encountered). Commit it here so its settings aren't silently lost.
+      if (currentSection.Name == Section.DefaultSectionName && currentSection.SettingCount > 0)
+      {
+        config.Add(currentSection);
+      }
     }
 
     private static string? ParseComment(string line, out int commentCharIndex)

Tests/SectionlessConfigTest.cs

@@ -0,0 +1,28 @@
+// Copyright (c) 2013-2026 Cem Dervis, MIT License.
+// https://sharpconfig.org
+
+using NUnit.Framework;
+using Assert = NUnit.Framework.Legacy.ClassicAssert;
+using SharpConfig;
+
+namespace Tests
+{
+  [TestFixture]
+  public sealed class SectionlessConfigTest
+  {
+    [Test]
+    public void SectionlessFileKeepsSettings()
+    {
+      var cfg = Configuration.LoadFromString("Setting1 = Value1\nSetting2 = Value2");
+
+      Assert.AreEqual(2, cfg.DefaultSection.SettingCount);
+      Assert.AreEqual("Value1", cfg.DefaultSection["Setting1"].StringValue);
+      Assert.AreEqual("Value2", cfg.DefaultSection["Setting2"].StringValue);
+
+      // Round-trips without gaining a section header.
+      var saved = cfg.SaveToString();
+      Assert.IsFalse(saved.Contains('['));
+      Assert.AreEqual(2, Configuration.LoadFromString(saved).DefaultSection.SettingCount);
+    }
+  }
+}