Ooops. $NEED_UPGRADE must be 0 by default. build_urlencoded does not utf8_upgrade
missed to add test
suggest W::F:U::XS 0.19
Checking in changes prior to tagging of version 0.19.

Changelog diff is:

diff --git a/Changes b/Changes
index bd304e0..bf592da 100644
--- a/Changes
+++ b/Changes
@@ -2,6 +2,10 @@ Revision history for Perl extension WWW-Form-UrlEncoded

 {{$NEXT}}

+0.19 2014-04-30T03:26:43Z
+
+   - bugfix: PP::build_urlencoded should not do utf8::upgrade.
+
 0.17 2014-02-24T13:50:55Z

     - fix EXPORT bug. _arrayref did not export