Enabling compress CSS causes fonts to change in Safari

I have a site I am planning on moving to a zen based theme. When I enable CSS compression and aggregation in the Administer > Site Configuration > Performance panel the site no longer renders properly in Safari.

All text on the site enlarges, as if a text-size: 110% or such item has been added.

This occurs in Safari v2.0.4 (latest non-beta version), and in v3 on both the Mac and Windows XP.

This issue does not occur with Firefox or IE 7.

This issue also does not occur with the Garland theme, which my current live theme is based on.