default error_log has zero level, the bug has been introduced in r2447
diff --git a/src/core/ngx_cycle.c b/src/core/ngx_cycle.c
index cdebf56..55d7c2d 100644
--- a/src/core/ngx_cycle.c
+++ b/src/core/ngx_cycle.c
@@ -168,6 +168,7 @@
         return NULL;
     }
 
+    cycle->new_log->log_level = NGX_LOG_ERR;
     cycle->new_log->file->name = error_log;