It is tricky, as there is a radio button like the little ones on the smilies below
in the delete window.

You click on edit, when the window opens you go to advanced, and this brings up the posting window like when you make a new post.
Delete is in there someplace, so you click delete and then at the bottom
comes the choices...
Do not delete this post
delete this post both with the little radio buttons

It defaults to do NOT delete..so you have to click the DELETE one.
It is like the deleting of your profile picture and avatar. And I guess it is
this way so you don't accidently do it when you don't mean to.

I have done it twice.. when I realized a double posting. And one recently, so
it should work.