do not replace subject if message format 1.x and unencrypted subject is enabled

src/message_api.c

@@ -2754,9 +2754,13 @@ DYNAMIC_API PEP_STATUS encrypt_message(
         else {
             // hide subject
             if (enc_format != PEP_enc_inline && enc_format != PEP_enc_inline_EA) {
-                status = replace_subject(_src);
-                if (status == PEP_OUT_OF_MEMORY)
-                    goto enomem;
+                // do not replace subject if message format 1.x and unencrypted
+                // subject is enabled
+                if (!(wrap_type == PEP_message_unwrapped && session->unencrypted_subject)) {
+                    status = replace_subject(_src);
+                    if (status == PEP_OUT_OF_MEMORY)
+                        goto enomem;
+                }
             }
             if (!(flags & PEP_encrypt_flag_force_no_attached_key))
                 added_key_to_real_src = true;