diff --git a/goini.go b/goini.go
index 510f217..ad2b8eb 100644
--- a/goini.go
+++ b/goini.go
@@ -152,7 +152,7 @@ func (ini *GoINI) SetString(name string, key string, value string) {
 	if index, ok := ini.findSectionKeyLineIndex(name, key); ok {
 		ini.fileLines[index].keyValue = value
 		ini.fileLines[index].modified = true
-		ini.rebuildIndexes()
+		ini.sectionValues[name][key] = value
 		return
 	}
 	ini.ensureSectionLine(name)
diff --git a/internal.go b/internal.go
index 12eedec..afd5aac 100644
--- a/internal.go
+++ b/internal.go
@@ -68,6 +68,9 @@ func parseRawLine(rawLine string, sectionName string) (iniLine, string) {
 		line.sectionName = nextSection
 		return line, nextSection
 	}
+	if strings.HasPrefix(trimmed, "[") && strings.HasSuffix(trimmed, "]") {
+		return line, sectionName
+	}
 	if parsed, ok := parseKeyValue(rawLine); ok {
 		line.kind = lineKeyValue
 		line.keyName = parsed.key
@@ -234,6 +237,9 @@ func (ini *GoINI) findSectionInsertIndex(sectionName string) int {
 	insert := len(ini.fileLines)
 	for i, line := range ini.fileLines {
 		if line.kind == lineSection {
+			if current == sectionName {
+				insert, _ = ini.commentRangeBefore(i)
+			}
 			current = line.sectionName
 			if current == sectionName {
 				insert = i + 1
@@ -250,9 +256,13 @@ func (ini *GoINI) findSectionInsertIndex(sectionName string) int {
 func (ini *GoINI) findRootInsertIndex() int {
 	for i, line := range ini.fileLines {
 		if line.kind == lineSection {
-			return i
+			start, _ := ini.commentRangeBefore(i)
+			return start
 		}
 	}
+	if len(ini.sectionKeys[ini.rootSection]) == 0 {
+		return ini.firstRootLineIndex()
+	}
 	return len(ini.fileLines)
 }
 
@@ -306,7 +316,11 @@ func (ini *GoINI) firstRootLineIndex() int {
 			return i
 		}
 	}
-	return 0
+	index := len(ini.fileLines)
+	for index > 0 && ini.fileLines[index-1].kind == lineBlank {
+		index--
+	}
+	return index
 }
 
 func commentLines(comment string) []iniLine {
@@ -337,8 +351,7 @@ func stripComment(comment string) string {
 	if !isComment(trimmed) {
 		return trimmed
 	}
-	trimmed = strings.TrimPrefix(strings.TrimPrefix(trimmed, "#"), ";")
-	return strings.TrimPrefix(trimmed, " ")
+	return strings.TrimPrefix(trimmed[1:], " ")
 }
 
 func renderLine(line iniLine) string {
@@ -360,10 +373,14 @@ func renderLine(line iniLine) string {
 
 func renderKeyValue(line iniLine) string {
 	separator := line.separator
-	if separator == "" {
+	if separator == "" || !strings.Contains(separator, "=") && strings.Contains(line.keyValue, "=") {
 		separator = defaultSeparator
 	}
-	return line.indent + line.keyName + separator + formatValue(line.keyValue)
+	value := formatValue(line.keyValue)
+	if strings.HasPrefix(line.keyName, "[") && strings.HasSuffix(value, "]") {
+		value = `"` + value + `"`
+	}
+	return line.indent + line.keyName + separator + value
 }
 
 func formatValue(value string) string {
@@ -392,7 +409,9 @@ func (ini *GoINI) formatString() string {
 		case lineKeyValue:
 			formattedLines = append(formattedLines, pendingComments...)
 			pendingComments = pendingComments[:0]
-			formattedLines = append(formattedLines, line.keyName+defaultSeparator+formatValue(line.keyValue))
+			line.indent = ""
+			line.separator = defaultSeparator
+			formattedLines = append(formattedLines, renderKeyValue(line))
 		case lineComment:
 			pendingComments = append(pendingComments, formatINIComment(line.text))
 		}