cached credentials for mapped drives and elevation

I have two computers, one running Windows Vista Ultimate and the other
running Windows Vista Enterprise. The first machine is configured on our
network but is set up within a workgroup. The second machine is configured
on our network as a member of our domain. Both machines have UAC turned on.

When I map network drives to the machines everything works normally.
However, when I run a program that requires elevation via a manifest, the
network drive mappings "disappear" in the login session that is created for
the elevated process on the Vista Enterprise machine. This results in the
elevated process not being able to "see" the same environment as the user
login session when an elevated process is run on Vista Enterprise.

Is there a difference in the default group policy that would affect the
caching of network credentials in Vista Enterprise? I recall that Windows
XP Media Center had network credential cache turned off by default so I
wondered if what I am seeing is something similar.

TIA

-Pete