QueryCache

After installing the needed components on the operating system and verifying that they do work I configured Qcache according the FAQ.
As I entered the final step to change the database handler from mysql to mysql_cached the site went blank. After browsing throw the FAQ it says I should copy /includes/database.backup.php over /includes/database.php. The file database.backup.php doesn't exist tho. After switching back to mysql as database handler, yea I did hit commit instead of save, everything seem to be in working order again.

The installed Qcache component is 1.5.0-rc2, Joomla! 1.5.14 - with various additions.

In the logs during my attempt I received this
"
PHP Notice: Undefined property: JRegistry::$db in <snip>/components/com_qcache/qcache.php on line 12, referer:<snip>

PHP Warning: include_once(<snip>/plugins/system/jfdatabase/intercept.jdatabasemysql_cached.php): failed to open stream: No such file or directory in <snip>/plugins/system/jfdatabase/jfdatabase_inherit.php on line 56, referer: <snip>

PHP Warning: include_once(): Failed opening '<snip>/plugins/system/jfdatabase/intercept.jdatabasemysql_cached.php' for inclusion (include_path='.:/usr/local/share/pear') in <snip>/plugins/system/jfdatabase/jfdatabase_inherit.php on line 56, referer: <snip>

PHP Fatal error: Class 'interceptDB' not found in <snip>/plugins/system/jfdatabase/jfdatabase_inherit.php on line 57, referer: <snip>
"

So there seem to be a fatal flaw in the Qcache component with missing or failure to redirect intercept.jdatabase ..