there is a change file for titlesec in bidi but since it is not yet complete and perfect, it is not loaded. Can you try a minimal file using just bidi and titlesec, no polyglossia, no arabxetex and see if this issue happens there too.
-- بسی رنج بردم در این سال سی عَجَم زنده کردم بدین پارسی
-------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex
