One of our users reported a problem with the text displayed on http://www.wdl.org/en/item/10643/. The author name on that page uses the Unicode combining half marks COMBINING LIGATURE LEFT HALF and COMBINING LIGATURE RIGHT HALF (U+FE20, U+FE21)
According to the Unicode 6.0 specification – see page 235-236 of http://www.unicode.org/versions/Unicode6.0.0/ch07.pdf – two adjacent marks should combine into a single curve.
On OS X, the behaviour depends whether font substitution occurred so e.g. the current WebKit Nightly will display the tests at http://chris.improbable.org/experiments/browser/combining-half-marks/ correctly only for Arial but most other fonts will display incorrectly.
Recent versions of Internet Explorer on Windows 7 or later display correctly in all cases. Chrome and Firefox are also inconsistent depending on the OS and font combinations.
Previously reported to Apple as rdar://13105608
Also happens in TextEdit with the same font, so likely not a WebKit issue.
This seem to work now.