Related to my #66532, but this one is probably the correct solution to my problem.
If I am holding down the button with my thumb to initiate a drag, and I move my finger across the clickpad, a scroll event is generated because of the two touch points.
Similarly, if I am preparing for a click and have my thumb resting on the clickpad, it should not be seen as a second touch.
This can be an option for Clickpads enabled like:
Option "IgnoreThumb" "<bool>"
Option "IgnoreThumbArea" "<L> <R> <T> <B>"
It seems that the clicked case is actually ok. It seems that I was getting scroll events in some cases because of some weird interactions with BottomEdgeArea, but once I use a config without the BottomEdgeArea, the clicked-finger is ignored ... so this is really just about ignoring the thumb that is just resting there in preparation to click.
Marking as dependency, see bug 66532#c3.
Downstream (Ubuntu): https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-synaptics/+bug/1026046
Should be fixed with Hans' patches leading up to c431d900f54696f608312ea51b1fa671839f7d42