Incorrect Quota Size

Have a Disk with a quota set to 500 MB.
This disk is set for users home drive, so every home
folder has a quota of 500 MB.
Problem is for some users when going into Quota Entries
there are some users which is saying the Amount Used is at
1 KB, when it is not. No matter how much data these users
have in their folders it still stays at 1 KB for Amount
Used.
Is there a way to fix this?