I recently performed a DBCC SHRINKFILE to shrink down the unused space from a datafile. Immediately afterwards I did an INDEX REBUILD to defrag all the fragmentation caused by the shrink command. Afterwards I noticed that the datafile had been enlarged back to it's original size. When I re-completed the same task of doing another DBCC SHRINKFILE but this time I used INDEX REORGANIZATION the fragmentation was removed and the datafile did not enlarge back to it's original size. Why?