Why richtextbox in C# when use unicode character move place in line on win xp

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C#

RichTextBox

hi my program work correctly on windows 7 and later but on windows xp don't work correctly

when type "/,-" on English language this work correct but on Persian Language this incorrect work
for sample in English language :

2012/02/02

in Persian Language work this:
02/02/2012

What I have tried:

i have write in Richtextbox when language is Persian like this " 2012/02/02 "
how do it?