v 5.1.7, win XP and Win 7, Safari only; Ok on Chrome.
Text is rendered incorrectly when a stroke is specified. Multiple artefacts are visible (shadowing, gaps, and so on). This jsfiddle (http://jsfiddle.net/JgS4T/) renders correctly on FF, Chrome, Opera, and IE9. You may need to zoom the browser window in Safari to make the artefacts more visible. The artefacts are sometimes much more obvious than in this simple test case; text with stroking is unusable in general.
Could you please attach a screenshot of bad rendering?
It looks fine to me on Mac, but maybe I'm missing something.
Created attachment 145443 [details]
Screenshot from Windows 7, Safari 5.1.7 (most recent for Windows; 7534.57.2)