There definately seems to be some issues with including or requiring files from within other files that have been included in the same fashion.  Say I have a file called "test.php" in the docroot that includes "file1.php".

The included file contains some class definitions which inherit from classes defined in "file2.php", so at the top of "file1.php" I have:

include_once("file2.php");

This does not seem to work.  It is finding the file correctly, but I receive "Cannot inherit from undefined class" errors.  If I manually include "file2.php" within the "test.php" file along with the "file1.php", it works fine.

Is this meant to happen, or is it a bug or known issue?