Comment 9 for bug 934184

That seems the same issue than bug #934770

the change was discussed described by Chase on
https://lists.ubuntu.com/archives/ubuntu-desktop/2012-February/003694.html

"* When the user checks "Enable mouse clicks with touchpad", I believe
the "Synaptics Locked Drags" setting should be true.
...
If it's not entirely clear what the change is, try setting the property
and playing with it. Enabling the property resolves the problem of
trying to drag farther than your touchpad is wide or tall."

Reassigning to xserver-xorg-input-synaptics