after you check your post for HTML error with W3C validator, W3C is creating a clean up and a valid version of your post after that...can you just copy paste the clean version to replacing your post just like that? or you must configure your post again? thanks!
Usually you should not copy paste, as it shows generated/rendered code, and things like dynamic php scripts etc won't be available in the W3C version. They should only be used as reference to clean your original source code.