I ended up having the [mudslide:...] shortcode as plain text in the excerpts (the excerpts are being generated automatically).
It's not the case with other plugins, e.g. [youtube...] doesn't appear in the excerpt, only [mudslide] does.
strip_shortcode() is responsible for removing those [] tags. The problem is, [mudslide] is not among the preg_replace pattern and therefore strip_shortcode will not remove it.
Here is a quick fix: edit mudslideshow.php and paste this near line 100
add_shortcode('mudslide', 'shortcode_mudslide' );
function shortcode_mudslide($atts, $content = null) {}
btw, thanks for the great plugin, it works brilliantly