When assigning a string that contains a "replacement variable"-like sub-string to an actual replacement variable, on IT's next "pass" it will replace the variable-like sub-string with nothing and if this string was contained within a block it will remove the block:

Example
Lets assume for some unknown reason the programmer wishes to print name like this -> {name}

<code>
<?php

require_once("HTML/IT.php");

$vars["title"] = "Welcome! {Adam}";
$vars["content"] = "This is some content!";

$template = "
<!-- BEGIN TITLE -->
{title}<br />
<!-- END TITLE -->
<!-- BEGIN CONTENT -->
{content}<br />
<!-- END CONTENT -->";

$tpl = new HTML_Template_IT;
$tpl->setTemplate($template, TRUE, TRUE);
$tpl->setVariable($vars);

echo $tpl->get();

?>
</code>

When the above template and data is processed by IT it will not print the name contained in the string $vars["title"].

I hope this is enough info to figure out what's up :)

Adam