/usr/bin/lastlog only displays local user entries. Why?

I have a Debian Squeeze server, joined to an AD domain. When I run /usr/bin/lastlog, it only displays entries for local users (the ones in /etc/passwd). However, AD accounts can also log in, and if I run 'lastlog -u some_AD_user', it happily gives me the last login info for that user - so that info is in the lastlog database. It just doesn't display when I run 'lastlog' alone, nor if I specify a range of UIDs (the range only seems to work for local accounts).

Anyone know why?

Thanks