I'm guessing you didn't actually encode the text you place in your feed.

$ perl -MHTML::Entities -MXML::LibXML -E'
   $xml="<root>".decode_entities("&eacute;")."</root>";
   utf8::encode($xml);
   XML::LibXML->new->parse_string($xml);
   say "ok";
'
ok

$ perl -MHTML::Entities -MXML::LibXML -E'
   $xml="<root>".decode_entities("&eacute;")."</root>";
   #utf8::encode($xml);
   XML::LibXML->new->parse_string($xml);
   say "ok";
'
:1: parser error : Input is not proper UTF-8, indicate encoding !
Bytes: 0xE9 0x3C 0x2F 0x72
<root>?</root>
      ^
[download]