Migrating tables to new tablespace, freed up space doesn't match moved data

Hi all,

I've set up a tablespace on a different partition from the main data
directory. I moved a few tables and indexes over to the new tablespace
and the disk space used in this new tablespace doesn't match the amount
of data 'freed up' from the main data directory. The tablespace is
sitting at 15 GB used, but the space freed up on the main partition is
about 10 GB.

Any thoughts as to why I didn't see as much space freed up as I thought
I would?

Thanks,
- Brian F