Does the 6.3 vim global file turn on syntax highlighting or not? If 6.2 does, or you added that, and 6.3 doesn't it would look like it's forgotten you have a colour terminal.
The other thing is that the rules might have changed slightly for telling the syntax highlighting that you can do colour based on your TERM setting. I remember having that problem within screen somewhere when my TERM when slightly funny after an SSH.
Wade.