Drop Tablespace x including contents and datafiles does not remove files

 I've set up databases using Oracle 10g patch 10.2.0.4.0 including tablespaces on servers using Windows XP. Some of the scripts I test need to remove and re-create tablespaces, which works fine for ASM managed data files, but is not working properly for locally managed (operating system) files.

When I drop the tablespaces with the following script, sometimes the data files are not removed:

DROP TABLESPACE mytablespace INCLUDING CONTENTS AND DATAFILES;

After executing this command, the dba_data_files view shows the associated data files are gone, but the physical files are still there.  Next time I re-create the tablespaces, I get failures because the files collide with the new datafiles I am attempting to create.