Adding additional test suggested by nikic.

lib/Twig/Lexer.php

@@ -118,6 +118,7 @@ class Twig_Lexer implements Twig_LexerInterface
             $tmpPos = strpos($this->code, $this->options[$type][0], $this->cursor);
             if (false !== $tmpPos && $tmpPos < $pos) {
                 $trimBlock = false;
+                $append = '';
                 $pos = $tmpPos;
                 $token = $this->options[$type][0];
                 if (strpos($this->code, $this->options['whitespace_trim'], $pos) === ($pos + strlen($token))) {

test/Twig/Tests/Fixtures/tags/trim_block.test

@@ -28,6 +28,8 @@ Whitespace trimming on tags.
     {%- endif -%}  
     </ul>
 after
+{{ 5 * '{#-'|length }}
+{{ '{{-'|length * 5 + '{%-'|length }}
 --DATA--
 return array('leading' => 'leading space', 'trailing' => 'trailing tabs', 'mixed' => 'mixed tags', 'both' => 'both')
 --EXPECT--
@@ -46,4 +48,6 @@ return array('leading' => 'leading space', 'trailing' => 'trailing tabs', 'mixed
     <ul>
         <li>both</li>
     </ul>
-after
+after
+15
+18