Large profiles show size as ?

I'm running Vista 32-bit RC2. If I go to properties of Computer, Advanced
system settings, Advanced tab, click on the settings button for user
profiles, of the three profiles there, the two that are over 20Gb in size,
which includes the profile for the logged in user, just show a question mark
for the size field. The third user profile shows the correct size of 17.5Mb.
I got the sizes by running Windows Explorer as administrator and looking at
the properties of each user folder under c:\users.

I don't know at what point in size it stops showing the correct value. Maybe
there is a 32-bit value being used and it craps out at 4Gb. The majority of
the size used in both large profiles is several thousand digital images in
both.

Nick