Server 2003 Disk Quota not working

Hi,

Am running Windows Server 2003 SP2 and it seems that disk quota isn't
working like I think it should. We have a volume (D which acts as a
file server volume. So, our employees each have their own share there
that they can access via browsing from their PC to \\file-server-name
\first-initial-last-name

I've set the disk quota on volume D: like this:

Enable quota management is checked
Deny disk space to users exceeding quota limit is checked
Limit disk space to 5GB
Set warning level to 4.5GB
Log event when a user exceeds their quota limit is checked
Log even when a user exceeds their warning level is checked

My folder, for example, is over 5GB, but I can still add things to
it. So, am I misunderstanding how this should work? Or, is it really
just broken?