In Microsoft SQL Server I can go into Database Properties > Files and change the Size of a file to a lower number. If there's space available, it will actually reduce the file's size, and never tells me it's running a shrink command or anything like that.

What is happening there? Am I successfully lopping off unused space without reorganizing any pages, as the interface seems to suggest? Is it running a DBCC SHRINKFILE in the background, possibly in TRUNCATEONLY mode?
