If you do is_really_writable() on a file that does not exist on a Windows server or on a Unix box with safe_mode enabled, it will create the file and leave it there. Fixes #80
diff --git a/system/core/Common.php b/system/core/Common.php
index cd6b933..f424a2c 100644
--- a/system/core/Common.php
+++ b/system/core/Common.php
@@ -88,7 +88,7 @@
 			@unlink($file);
 			return TRUE;
 		}
-		elseif (($fp = @fopen($file, FOPEN_WRITE_CREATE)) === FALSE)
+		elseif ( ! is_file($file) OR ($fp = @fopen($file, FOPEN_WRITE_CREATE)) === FALSE)
 		{
 			return FALSE;
 		}