Ubuntu 17.04 middle mouse button problems

[Jeffery Small]

I've posted this to all the hardware and software development groups and
Ubuntu forums and received no replies so I'm trying here to see if anyone
else has seen this problem.

System: Desktop dual-Xeon CPU, 32GB RAM, Nvidia Quadro K4000 video,
Sun USB keyboard and mouse.

Everything was working fine for years up through Xubuntu 16.10.  I
upgraded to Xubuntu 17.04 and my middle mouse button behavior has changed
drastically.

I have a standard USB three-button Sun mouse with no scroll wheel.  In
the past I have had full control over the use of the middle button.  For
example, I use the All-in-One Gestures add-on in Firefox to perform middle
mouse button actions and I do the same thing with my CAD program running
under Windows 10 in a KVM virtual window.  After the OS upgrade, the middle
button is now being preempted and used for a pseudo scroll-wheel function.
Hold-and-drag scrolls the content in most windows.  For example, I can
still paste the current selection into an xterm/xfce-terminal using a B2
click, but B2 hold/drag scrolls the past content in the terminal window!

Since it affects apps directly and transfers through the VM to a different
OS, this must be due to some low level change in Linux, Xfce4, or the
mouse driver.  I have searched for documentation on this change and found
nothing.  I do not see any option for this mouse behavior in the settings
menus.

Here is some additional info:
-------------------------------------------------------------------
% xsetpointer -l
2: "Virtual core pointer"	[XPointer]
3: "Virtual core keyboard"	[XKeyboard]
4: "Virtual core XTEST pointer"	[XExtensionPointer]
5: "Virtual core XTEST keyboard"	[XExtensionKeyboard]
6: "Power Button"	[XExtensionKeyboard]
7: "Power Button"	[XExtensionKeyboard]
8: "Device 2Port KVMSwitcher"	[XExtensionKeyboard]
9: "HID 0430:0100"	[XExtensionPointer]
10: "HID 0430:0005"	[XExtensionKeyboard]

The Mouse and Touchpad settings menu lists the active mouse as item #9
above: HID 0430:0100
-------------------------------------------------------------------
The relevant section from /etc/X11/xorg.conf:

Section "InputDevice"
    # generated from default
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "auto"
    Option         "Device" "/dev/psaux"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection

This has not changed since before the OS upgrade.  However, maybe there is
something that could be set here.  I wonder if Emulate3Buttons needs to
be changed to "yes"?  Documentation on this is skimpy.
-------------------------------------------------------------------

Can anyone else confirm that they have also seen this behavior and are
there any pointers as to how I can go about restoring the original
functionality?  This is seriously screwing up my use of the machine and
any help would be greatly appreciated!  :-)

Thanks.
--
Jeff