Working copy is preserved?

I'm setting up Workgroup PDM at our company. I'm fiddlingwith the revisioning scheme now, and what puzzles me is the Workingcopy revision. I understand the reason for Working copies is tosave disk space. The SW Workgroup PDM help says the following:
"The vault retains a copy of every revision except for Working copyrevisions."

Still, all the old Working copies are left in the vault's projectfolder. Shouldn't they've been deleted when incrementing to thenext revision? Currently, using Working copies doesn't seem to savedisk space that much. Is this a bug or am I missing something here?

SolidworksWorkgroup Pdm