The LispWorks editor currently relies on integral font sizes. Some Mac OS X fonts have non-integral size and will be displayed incorrectly in the Editor and Listener tools and other uses of
The solution is to use a font with integral size. The following are known to work: Monaco 10, Monaco 15, Monaco 20.
Select the font for Editor and Listener tools by LispWorks > Preferences... > Environment > Styles > Editor Font .
LispWorks Release Notes and Installation Guide - 23 Dec 2011