It appears to me that when you preview, the html code (e.g. to put in a web site link) is not made active - you see the raw code not the link as you want it to be. Then when you submit the html works properly (as long as no typos). It would be nice if the html would work in the preview, then you would know you had done it right before submitting.
Similarly, but less of a problem, the signature is not attached in the preview.