Question about portsdb (part of ports-mgmt/portupgrade)

Sat Jun 22 12:34:56 UTC 2013

On 9.1-RELEASE, when I follow 'portsnap fetch update' with 'portsdb -u', 
it updates the INDEX-9 and INDEX-9.db files in /usr/ports for me.

But the corresponding action doesn't happen on 10.0-CURRENT (r251572) 
until I do a 'portsdb -Fu'.

Why the difference? Obviously it's no big deal, but I'm rather curious. 
This is portupgrade-2.4.10.5_1,2 in both cases, by the way.