On WordPress 3.5, I made a post that contained both a link to a slideshare presentation on its own line, and the [slideshare ...] shortcode.
Without this plugin enabled, the "own line" link to slideshare perfectly embedded, and I saw the "[slideshare ...]" text on the screen - which is, of course, expected behavior.
WITH this plugin enabled, the shortcode continues to be turned into an embed, however, the native slideshare embedding is broken, and there is no output at all, other than these notices:
Notice: Undefined variable: new_html in /data/apache/lamp/dev4-ces-lamp/docs/wp-content/plugins/slideshare/slideshare.php on line 179
Notice: Undefined index: w in /data/apache/lamp/dev4-ces-lamp/docs/wp-content/plugins/slideshare/slideshare.php on line 136
My suggested fix would be something like this inside v2.0 of your plugin:
If wp_version >= 3.5, replace [slideshare ...] code with normal text links to the slideshare, and let WP handle the rest
if wp_version < 3.5, keep on keepin' on (like before)