I install sql server 2005 sp3 and run command DBCC SHRINKFILE <datafile>

please refer the following links for more information

http://www.sqlserverdba.co.cc/2009/05/move-contents-between-files-within.html

http://technet.microsoft.com/en-us/library/ms189493.aspx

http://support.microsoft.com/kb/907511

Are you using updated SQLServer SP3? I think it has some bug fixes for deallocate of ntext,image columns when shrink data files.

Three months back, I had similar issues, I tried...