Okay so this is what happens for me.
I write a blog post then as a user I post on the blog (once) it comes up as the comment has been posted twice. When I refresh the page nothing changes.
In the forums though the comment only shows as being posted once.
When I post a comment in the forum it does it correctly however on the blog post (in the comments) the comment from the forum is doubled.
And the original comment (the blog comment I made) is fixed and put back correctly.
Also the time and date can be messed up.
The way this happens is pretty sporadic.
Hope that helps.