Comment 44 for bug 133060

Well, i think that the line just above is responsible : SelectTapButton(priv, edge);

it will detect that the tap is made in the bottom left corner, and by default, corner taps are disabled. hopefully, corner taps can be configured with your graphical interface or with xinput.

if you want to test if this applies to you, do :

# aptitude install xinput if that's not already installed
xinput list
# note the id of your synaptics device, for example, id=20
xinput set-props 20 "Synaptics Tap Action" 0 0 0 3 1 0 0

now tap in the middle of your pad. the taps that i think aren't recognized should now be recognized as right clicks. If that's the case, then this can be easily fixed, either use
xinput set-props 20 "Synaptics Tap Action" 0 0 0 1 1 0 0
to make those tap recognized as left clicks, or patch the source to add the line
edge = edge_detection(priv, priv->touch_on.x, priv->touch_on.y);
before SelectTapButton(priv, edge);

(note : the xinput command affects the mouse button to use under different tap configuration :
xinput set-props [ID] "Synaptics Tap Action" [RT] [RB] [LT] [LB] [F1] [F2] [F3]
[RT] is the mouse button to use when tapping on the right top hand corner
[RB] [LT] [LB] on the right bottom hand corner, left top hand corner, left bottom hand corner ...
[F1] tapping on the center with a single finger
[F2] tapping with two finger
[F3] tapping with three finger
0 disable the tap, 1 is the left button, 3 the right button and 2 the middle button.
)