kcachegrind having difficulties to link php xdebug calls

I'm using XDebug to generate profile repport. The profile are generated, but I'm unable to create a complete call graph using kcachegraph.

The XDebug config is:

zend_extension=/usr/lib/php5/20090626+lfs/xdebug.so
xdebug.profiler_enable = 1
xdebug.profiler_output_dir = /var/www/xdebug/
xdebug.profiler_output_name = cachegrind.out.%t-%s
xdebug.profiler_enable_trigger=1

When I open the repport in kcachegrind, it seems to works, except that somt call seem in double, with one of the two having a location: (unknown).

Note that index.php only have 1 line of actual code, that is a require to the front controller. No autoloading at this stage of the execution, so I really can't figure out why I have 2 require::frontcontroller.php.

Here's a screenshot of 3 windows that might help you:
http://img46.imageshack.us/img46/2226/kcachegrind123.png

Any clue on what could be the problem ?

Thanks