filenamesearch doesn't find

[mimo]

When using the Find in dolphin to search through the content of files it often doesn't find content when it exists. E.g.

fgrep -R taxonomy_terms_per_page_admin /var/www/drupal/drupal7/modules/taxonomy/
/var/www/drupal/drupal7/modules/taxonomy/taxonomy.install: variable_del('taxonomy_terms_per_page_admin');
/var/www/drupal/drupal7/modules/taxonomy/taxonomy.admin.inc: $page_increment = variable_get('taxonomy_terms_per_page_admin', 100); // Number of terms per page.

Whereas filenamesearch with FInd:taxonomy_terms_per_page_admin, Content, From here (taxonomy) returns "No items found"

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: dolphin 4:4.6.5-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-13.53-generic 2.6.38.8
Uname: Linux 2.6.38-13-generic x86_64
Architecture: amd64
Date: Tue Jan 31 12:06:08 2012
ProcEnviron:
 LANGUAGE=
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: kdebase
UpgradeStatus: Upgraded to natty on 2011-10-20 (103 days ago)