Context Sensitive (?) $vbphrase usage?

[David LeBow]

In the Navbar template I have added code to create submenu headings using $vbphrase.

Here's a snippet:

<tr>
<td class="thead">$vbphrase[forum_tools]</td>
</tr>

On some pages (e.g.: within forums), this item displays just fine. On others (notably index.php), the string does not expand, making my menu header disappear. But... not on all pages.

I've had the same problem with other texts. For example, $vbphrase[new_posts_nav] seems to work ONLY on Index.php but not when within a forum.

Are there restrictions as to which phrases can be used where..?