Oracle Database Discussions

Hi all,
I am doing some kind of testing in my test maching and I faced the following situation.

I have a good control file and all the archives starting from the 1st scn. Now I brought down the instance and physically deleted a datafile and tried bringing up the db. This time it couldnt open the db as a file is missing, so I created the datafile and gave the recover database command and things opened up fine. No I backed up the ctrl file to trace and brought down the instance. Now I deleted my controlfile and recreated it successfully by using the script that I got from trace and tried the datafile drop and recreate trick as before, but in this case I couldn't create the datafile. Can anybody explain me why is this behaviour?