Re: is it bug or not?

> and radiusd does not recognize the it as duplicate

Recognition of duplicates is based on the value of request
identifier and authenticator. In your case failure to recognize
the duplicates means that the NAS has changed the identifier
or the authenticator (or both) between the requests. Enabling
debugging level "radius.c"=1 will show which of the items has changed.
To work aroung the problem you will have to use extended comparison.
For more info, please refer to

http://www.gnu.org/software/radius/manual/html_chapter/radius_6.html#SEC16

and

http://www.gnu.org/software/radius/manual/html_chapter/radius_9.html#SEC74

Regards,
Sergey