A poster in the Apple Support Communities has pointed out that most Apple Arabic fonts in Mavericks will not display certain vowel sign sequences correctly, include the default Geeza Pro.
My initial testing indicates that Waseem and Diwan work, as well as some English fonts that happen to include Arabic, like Courier New. Others are the SIL fonts Lateef and Scheherazade.
My initial testing indicates that Waseem and Diwan work, as well as some English fonts that happen to include Arabic, like Courier New. Others are the SIL fonts Lateef and Scheherazade.