Remove the layout and ensure both fields are displaying fine. If they are then there's a possible issue with your layout usage. I can't make any sense of that HTML. Is that the HTML output by the Gravatar field when using an email address with no gravatar attached to it? Invalid email address seams to work fine for me and just outputs the default gravatar as follows.
Code:
<img src="http://www.gravatar.com/avatar/ce8cd946b79b19efccc42d6843d4fce4?s=200" alt="Gravatar" title="Gravatar" class="cbImgPict cbFullPict img-thumbnail">
The [cb:userfield field="cb_gravatar" /] usage will output the layout parameter usage of the gravatar field so be careful what you add to the layout parameters of the gravatar field. I assume your layout usage should only be on the avatar field it self.