Postage Due 1986 - Flaw

The 50c postage due stamp showing below is one of the five postage due stamps issued on 15 September, 1986 (http://kajang-stamps.blogspot.com/2008/09/postage-due-1986.html). A minor flaw has been recorded on this 50c postage due stamps. The flaw (ring shape) occurs at the bottom of the "0".

Top: normal stamp; Bottom: flaw stamp
Ring shape appear at the bottom of the "0"