Comment 1 for bug 188387

I am experiencing the same symptoms on Hardy Heron.

In my touchpad InputDevice Section of '/etc/X11/xorg.conf', I added an 'Option "CorePointer" and restarted GDM. The double-clicking issue stopped, both with my external mouse and touchpad. I removed and added the Option (restarting GDM each time) to make sure it was the providing the option was having the effect I was seeing. All together, my InputDevice section looks like:

Section "InputDevice"
    Identifier "Synaptics Touchpad"
    Driver "synaptics"
    Option "SendCoreEvents" "true"
    Option "Device" "/dev/psaux"
    Option "Protocol" "auto-dev"
    Option "HorizScrollDelta" "0"
    Option "CorePointer" # This added line removes the undesired double-clicking.
EndSection

I am attaching my complete 'xorg.conf'.