USB mouse woes

Microsoft wireless USB mouse is completely non-responsive after boot.
Moving the mouse will produce a mouse cursor on syscons, but no movement
is observed.  Same mouse operates successfully on Ubuntu Linux 5.04 and
Windows XP, and also under FreeBSD with a USB-PS/2 adapter (via psm)

System info:

MSI KT800 Neo, VIA chipset

FreeBSD 6.0-CURRENT #0: Wed Jun 15 01:00:33 PDT 2005
    root_at_nail.lovett.com:/usr/obj/work/src.6/sys/NAIL
[...]
CPU: AMD Athlon(tm) 64 Processor 2800+ (1800.07-MHz K8-class CPU)
  Origin = "AuthenticAMD"  Id = 0xfc0  Stepping = 0
[...]
uhci0: <VIA 83C572 USB controller> port 0xc400-0xc41f irq 21 at device
16.0 on pci0
uhci0: [GIANT-LOCKED]
usb0: <VIA 83C572 USB controller> on uhci0
usb0: USB revision 1.0
[...]
[repeat for usb1, usb2, usb3]
[...]
usb4: EHCI version 1.0
usb4: companion controllers, 2 ports each: usb0 usb1 usb2 usb3
usb4: <VIA VT6202 USB 2.0 controller> on ehci0
usb4: USB revision 2.0
uhub4: VIA EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub4: 8 ports with 8 removable, self powered
[...]
ums0: Microsoft Microsoft Wireless Optical Mouse\M-. 1.0A, rev
2.00/0.17, addr 2, iclass 3/1
ums0: 3 buttons and Z dir.
[...]

"NAIL" kernel config is merely GENERIC with un-needed drivers.  Makes no
difference for any combinations of (uhci,ehci,usb,ums) compiled in to
the kernel, or as modules with appropriate loader.conf magic.

usbd is running (via /etc/rc.conf), and the appropriate moused on
/dev/ums0 is also running.

crw-r--r--  1 root  operator    7,  82 Jun 15 01:15 /dev/ums0

Any suggestions on further places to look to get the mouse working
appreciated.  Running under a base install of ports/x11/xorg reveals
similar breakage, both either via the SysMouse protocol, or direct
talking to /dev/ums0 as a USB mouse without usbd (and moused) running.

A quick look through the archives reveals a few other reports of similar
issues, but no resolution.

Ideas?

-aDe