firdavs_abc, I am having the exact same problem.
the Arabic pdf text is displayed perfectly when in small font (which is the pdf default size) only when I resize does the text become random like you said. My guess is that the reflowing mechanism is not working correctly with Arabic fonts. And this is mainly due to the right-to-left nature of the Arabic language. If there is anybody out there whose language is a right-to-left, and who was able to solve this problem on their sony reader please let us know.
firdavs_abc, would you kindly let me know if you find a solution to this problem.