Blog postDateTime Sorting

I have a blog and when I show the posts like this:

But when I edit a post, the post, no matter what the publish date, it brings the post to the top since it was last edited. Is there a way to sort by the publish date instead?

It looks like this, in post.html:

My question was actually inaccurate. What happens is that when CMS blog editors update a page, the date seems to reset. So when they go back and update the post date, it's fine and in order.

We later learned by trial and error that the users were switching the template after doing edits, which reset the date. So now if they start by resetting the template (I have new blog templates ready for older posts) then it's fine and the date doesn't reset. Thanks anyway on this one!