Arabic Diacritics move to unwanted places if you use an Index Marker in the same line
1. Adobe InDesign CC 14.0 (Middle Eastern version -- English يدعم العربية)
2. a. Type this Arabic text: شَيْء غريب
2. b. Create new Index entry for the second word: غريب
3. The Diacritics should stay as they were.
4. Diacritic of the second letter (يْ) goes somewhere else.
Hassaan Abdur Razzaaq commented
Also happens with footnotes and some special characters. RTL fonts with OpenType features are generally very buggy in InDesign. Even popular fonts like Traditional Arabic are almost unusable with diacritics. The Quranic fonts from nashr.qurancomplex.gov.sa also don't work.
These bugs have been around for more than half a decade. The Middle-Eastern features don't seem to have been touched since the days of WinSoft.