This is a side-effect of the (partial) fix to Related questions with over 99 score display incorrectly, which was resolved by preventing multi-digit question scores from wrapping onto multiple lines. However, now they overflow their boxes horizontally instead:

Adding the following extra CSS rules would fix the problem by making the boxes wider for three- and four-digit scores (like they are on SO, for example):
#sidebar .answer-votes.large { width: 32px !important }
#sidebar .answer-votes.extra-large { font-size: 11px !important; width: 32px !important }
(The !important
tags are only there because the existing styles use them. IMO, it would be better to clean up the CSS and get rid of them, as well as the fossil layers of conflicting rules that are their presumed raison d'être.)
The result would look like this:

(Ps. The second screenshot above is taken using SOUP, which already includes this CSS fix.)