included files cached??

does PHP or apache do some sort of caching when you use include()? I've had repeated problems with this using various Apache 1.3's and PHP4's. The page that include()s some included_file.php doesn't see any changes to included_file.php until i force it to "echo" something which "wakes up" the file. But this doesn't even always work. right now we are goiing crazy with this: main_file.php <? ini_set('display_errors',1); // trying to find the problem! include('/absolute_path/init_file.php'); ?> init_file.php <? include('/absolute_path/included_file1.php'); ?> <? include('/absolute_path/included_file2.php'); ?> included_file2.php <? echo "<h1>here I am!</h1>"; ?> we just added the line that includes include_file2.php (and the file itself). the site was already working for some time just fine. there is no warning or error with include_file2 - nothing happens. file_exists('/absolute_path/included_file2.php') returns true! anybody out there seen this?