Testing Moodle 1.6 beta 3.
In answer to Tim's question. This is a theme-related issue for which I suggest this solution: in your theme's styles_layout.css add the following lines
.que td.text,.que td.feedback {width:auto;}
See screen shot for visual aspect before and after applying my solution. NOTE.- I have used FF's WebDeveloper to Outline Table Cells (in red).
Joseph
PS In 1.6 beta 3 quiz pages display uses CSS from both \mod\quiz\styles.php and from standard theme CSS files, which I find a bit confusing.