In RSS Shortcode v0.1 Excerpt is never shown.
rss-shortcode.php line 26:
if ( $excerpt != false && $excerpt != "false") {
'$excerpt != false' will evaluate to 'true' or 'false' as excepted.
'$excerpt != "false"' will evaluate to 'false' if $excerpt is true since it's the wrong datatype. Use '!==' instead of '!=' there.
Patch rss-shortcode.php line 26:
if ( $excerpt != false && $excerpt !== "false") {