If I delete a latest post on a topic, then I go to forum where that topic was, it shows that post still is there in that where it shows who has made last post in topic.

Hm, that may be little confusing. There is simpler version:

• Admin goes to forum A.
  

• Last post-thing says user B has written last message in thread C.
  

•  It is spamming message written by user B to Thread C in forum A.
  

• Admin deletes the spamming message of user B.
  

• Admin returns to forum A.
  

• It still says that user B has written last message in thread C.
  

• But if you press that last message of Thread C in forum A, it goes to last undeleted message that have been made by user D.
  

Um... Did you get it? Can that problem be fixed?

I don't know if it can be fixed, but when someone posts next, it will show up their name