I wonder if anybody has come across this problem and could help me to understand it further. I noticed that when the hamza diacritic (U+02BE) follows 'a' and the two are italicised, the hamza either gets thrown off or disappears. This occurs for a number of fonts when using the Adobe World-Ready composer in InDesign CS6, Windows 10.
The problem occurs for a number of fonts, including system fonts like Calibri (Microsoft), Arial (Monotype_, and Times New Roman (Monotype).
It doesn't make a difference whether using either the paragraph or single-word version of the World-ready composer.
The following image should make it clearer. I have also attached a PDF so you can copy and paste the words to see for yourself. As you can see the problem does not occur for the ayn diacritic (U+02BF). I have not managed to find any other problematic combinations so far.
Interestingly, the problem doesn't occur on a couple of modified fonts I tested...so perhaps the issue is down to kerning tables being copied from font to font and Adobe world-ready composer not interacting very well with them?
InDesign CS5, Adobe World-Ready composer, a & hamza (ʾ) problem