Can't su from rxvt

[John McAree]

Hi,

I'm currently running:
FreeBSD chimaera 6.0-CURRENT-SNAP004 FreeBSD 6.0-CURRENT-SNAP004 #0: Thu 
Jun  2 06:12:51 UTC 2005 
root at wv1u.samsco.home:/usr/obj/usr/src/sys/GENERIC  i386

(although the problem existed on FreeBSD 5.4-RELEASE, also).

I use rxvt (rxvt-2.6.4_1) when in X, and I am unable to su from it for 
some reason. If I `su -` or `su`, I'm prompted for root's password, 
however the authentication fails. If I'm logged in from the console, or 
running gnome-terminal, I can su to root just fine. Also, if I use rxvt 
and ssh out (to my laptop say), then ssh back, I can su just fine.

I'm incredibly confused. Does anyone have any idea why this could be 
happening?

Thanks in advance,
John.