Tip of the day:

When creating a template that is html or VF, users can't edit the body after they select it. This can be good and bad at the same time.

A work around is to use plain text. For VF templates use

<messaging:plainTextEmailBody >

</messaging:plainTextEmailBody>

in place of

<messaging:htmlEmailBody>

</messaging:htmlEmailBody>

You loose some formatting, but the apex part works.