Yes, it's annoying when we accidentally post twice. You have to be careful when you click the button and check to see if you have already posted. It happened to me early on too.

If you do, you just write 'POST ERROR' and delete the content. That way you don't get votes for the two posts.

Some people even say 'don't vote this post - posted in error' as the title.

I hope this explains things a bit better for you.