Windows XP SP2 Routing Issue with Cisco VPN 3005

Hi everyone. I seem to have an VPN issue with XP SP2.
We have a very simple setup. We have a switch that has our
Cisco 2620 Internet Router, Cisco PIX 515 Firewall, and
Cisco VPN Concentrator 3005 connected to it. We have two
internal subnets connected by a Cisco 2620 LAN router. The
primary subnet we use is 10.1.3.x and the subnet located
in another building is 10.1.2.x. Everything works great
and has been for a few years. The Cisco VPN 3005 is
configured for PPTP only. We have Windows 2000 and Windows
XP clients using the built-in Windows PPTP client to
connect to the VPN 3005. The VPN 3005 is located on the
10.1.3.x subnet. Once connected to the VPN they can
connect to machines on both the 10.1.3.x and 10.1.2.x with
no problems. In the Windows PPTP client properties we
leave the box unchecked under TCP/IP that says "use
gateway on remote network." This way they go through the
VPN connection to get to 10.1.2.x and 10.1.3.x and use
their ISP's gateway for everything else, like surfing the
web. Like I this has been the setup for the last few years
and it works great.
OK, I upgraded a few machines from XP SP1 to XP SP2
and ran into a problem. By the way, in this scenario the
XP SP2 clients have their XP firewalls turned off. The
clients connect to the VPN server just fine and can access
anything on the 10.1.3.x subnet but can not access
anything on the 10.1.2.x subnet. They can not even ping
machines on the 10.1.2.x subnet. When I checked the box
saying "use gateway on remote network" it works properly
but now all of their traffic is going through the VPN
connection and that is not desirable. I found a work
around for this issue. When the client logs in to the VPN
server he/she gets an IP address from our LAN DHCP server.
They get an IP in the 10.1.3.x subnet. If I leave the "use
gateway on remote network" unchecked, connect to the VPN
and get assigned 10.1.3.20 via DHCP, open a DOS prompt and
type route add 10.1.2.0 mask 255.255.255.0 10.1.3.20, I
can connect to the 10.1.2.x subnet. Problem is if they
reboot their computer the route is lost and they have to
manually enter in the route add command again. My big
question is why do Windows 2000 Professional and Windows
XP Professional SP1 clients have no problems connecting to
the 10.1.2.x subnet and the Windows XP Professional SP2
clients do? What did Microsoft change in SP2 to cause this
problem. If anyone has any suggestions on how I can get XP
SP2 clients to connect to the VPN server properly without
going through all of these hoops I would appreciate it.
Thanks for the help.