Sometimes your WordPress theme's CSS will be inherited by your SlideDeck, or jQuery has been loaded more than once(more info). We try to be as specific as possible with our CSS, but sometimes a theme can be overly specific and your SlideDeck will inherit some styles. For example, your font size might be too small or too large. All your images may have a border surrounding them inside your deck, just like in your posts, etc.
To fix this, just add an iframe=1 to your SlideDeck shortcode:
[SlideDeck2 id=1644 iframe=1]