Thank you for your quick response and fix. I confirmed that's OK now.
There's no empty line or others contents after <example>...</example> block.
diff --git a/lisp/org-exp.el b/lisp/org-exp.el
index 4637e8e..461ec3d 100644
--- a/lisp/org-exp.el
+++ b/lisp/org-exp.el
@@ -2666,7 +2666,7 @@ lang=\"%s\" xml:lang=\"%s\">
(setq infixed t)
(insert "<pre>\n"))
(insert (org-html-protect (match-string 1 line)) "\n")
- (when (and lines
+ (when (or (null lines)
(not (string-match "^[ \t]*\\(:.*\\)"
(car lines))))
(setq infixed nil)