Fix

lib/widgets/controller.dart

@@ -91,7 +91,10 @@ class QuillController extends ChangeNotifier {
           delta.isNotEmpty &&
           delta.length <= 2 &&
           delta.last.isInsert;
-      if (shouldRetainDelta && toggledStyle.isNotEmpty) {
+      if (shouldRetainDelta &&
+          toggledStyle.isNotEmpty &&
+          delta.length == 2 &&
+          delta.last.data == '\n') {
         // if all attributes are inline, shouldRetainDelta should be false
         final anyAttributeNotInline =
             toggledStyle.values.any((attr) => !attr.isInline);