Leap 42.1 GNOME and proprietary Nvidia drivers.

I'm seeing an issue where when two users are logged in to the same machine, corrupted bits of user A's desktop appear on the desktop background of user B's session, or on the GDM Screen Shield that's over the lock screen for user B's session. It's difficult to describe. I've put a screenshot of what I'm talking about at http://paste.opensuse.org/65432157 It's of a session on tty2 logged in as user A. The bit of Firefox window visible on the Desktop background in that screenshot is from the session of user B that's on tty7.

Does anyone else see this? I've no idea if it's an openSUSE, GNOME, or Nvidia issue, or some combination of those. I haven't found any references to it online, but maybe I'm not putting the rights terms in to Google. I struggle to describe the problem so maybe other people do too.

Restarting GNOME Shell (Alt-F2 then entering r) results in the corrupted background being replaced with the user's chosen Desktop background.

I also find that sometimes that after unlocking a user's session, the Desktop background will be entirely black instead of the user's chosen Desktop background. Restart GNOME Shell also rectifies that.

me@mine:~>cat /etc/os-release 
NAME="openSUSE Leap"
PRETTY_NAME="openSUSE Leap 42.1 (x86_64)"
me@mine:~>rpm -qa | grep -i nvidia
me@mine:~>/sbin/lspci -vvnn | grep -A14 "VGA compati"
01:00.0 VGA compatible controller [0300]: NVIDIA Corporation GF106 [GeForce GTS 450] [10de:0dc4] (rev a1) (prog-if 00 [VGA controller])
    Subsystem: ASUSTeK Computer Inc. Device [1043:8365]
    Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
    Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 0
    Interrupt: pin A routed to IRQ 29
    Region 0: Memory at dc000000 (32-bit, non-prefetchable) [size=32M]
    Region 1: Memory at d0000000 (64-bit, prefetchable) [size=128M]
    Region 3: Memory at d8000000 (64-bit, prefetchable) [size=64M]
    Region 5: I/O ports at d000 [size=128]
    [virtual] Expansion ROM at de000000 [disabled] [size=512K]
    Capabilities: <access denied>
    Kernel driver in use: nvidia
    Kernel modules: nouveau, nvidia_drm, nvidia