I've actually found a sort of workaround using the following code for my Transitions or Scene Breaks:
Code:
<div style="margin-left:1em;margin-right:1em;text-align:center;margin-top:1.5em;margin-bottom:1.5em"> — </div>
... this causes the scene break to be formatted without the negative l & r margins which I apply to my other text (in order to reduce Kindle's default margins)...