If you visit the testcase link, you should see the the One Ring inscription rendered in Tengwar. This appears to render correctly in Firefox 3.5/3.6a (tested OSX/Linux/Windows). It did not render in Webkit nightly or Safari 4 (tested Windows). FWIW. According to kov in #webkit, it crashes Epiphany but renders correctly (!) in "Arora" I will attach the file to this testcase.
Created attachment 32126 [details] demo of problem
Created attachment 32127 [details] This is a screenshot of QtWebkit, created by zecke, showing the font rendering correctly.
I just tested in Safari 4 under OSX, also renders correctly there. So definitely just a Windows bug.