In the U.S., numeric dates are usually displayed as %m/%d/%y. On the quiz review screen, the history dates are displaying %d/%m/%y instead (the default language is en_us_utf8).
We added a quiz.php file to the en_us_utf8 directory, and changed the timestr variable to display the month first. However, we found that 2-digit days are now getting preceded by a space. For instance, we're seeign dates like 09/ 14/07. Single-digit days display fine - e.g. 10/4/07.
It appears that the userdate() function in lib/moodlelib.php removes leading zeros from days, which is inserting a space before the day if there is no leading zero. This doesn't pose an issue if the day comes first in the format string, but it is a problem with U.S.-formatted dates.