Vinay,
This is based on OB08 exchange rate maintained and difference rate in different date.
This is exchange rate difference is basically difference between posting date value ( old Difference) and Foreign currency valuation date ( f.05 run date).
If you see your exchange rate column it will be clear. For example take line item 1 from your example
Say on posting date 27.06.2013- Exchange rate =003852 ( Old value)
F.05 execution date ( Foreign Currency valuation)- Exchange rate= 003894 ( New Value)
so old difference was zero as old value was the same however the new value changed after F.05 so the new difference is now 422-.
I hope it clears your doubt.
Best regards
Hrusikesh