In the theme options there is a Blockquotes section. If you add
HTML Code:
display: table;
into that section it may take care of your issue. The box will then look something like the following.
HTML Code:
color: #555555;
padding: 1em 1em;
background: #f4f4f4;
border: solid 1px #e1e1e1;
display: table;