Weird image.php problem
 

This week i've uploaded image.php file several times but i still couldn't find a permanent solution. I uploaded it in ASCII mode yesterday and today when i go to mysite.com/image.php it displays the php content of the file. Re-uploading the file and hard refreshing with CTRL + F5 at the browser side displays a small vBulletin image as supposed to be.

We have guest posting allowed at our forums (moderated) and i think there are too many requests for image.php (verification image). I even tried to CHMOD image.php to 444 but it didn't help. Any ideas?