Cloudstack 3.0.2 and xenserver 6.0.2 don't delete snapshot on primary storage issue

[jerry]

recently we find out cloudstack 3.0.2 don't delete snapshot on primary storage 
after snapshot has been create d and copied  to secondary storage  on 
Xenserver,so  it is a big issue when we use recurring snapshot function,it 
occupied primary storage size??Does someone meet this issue ,any suggestion.

 Thanks