Why got XEvent type 84 in _x11_fd_callback?

[Leslie Zhai]

In geis-2.2.16, libgeis/backend/grail/geis_grail_backend.c source code file, about the 1143 line,
http://bazaar.launchpad.net/~oif-team/geis/trunk/view/head:/libgeis/backend/grail/geis_grail_backend.c#L1147
it would get error XEvent type, printf the XEvent type is 84.

My development enviorment shown as below:
3.12.7-2-ARCH i686
xf86-input-synaptics-1.7.3
geis-2.2.16
touchegg svn reversion 189
gnome-shell 3.10.2

I used touchegg, a qt4 gesture recognition application based on geis, to debug gesture recognition,
and my touchpad supports multitouch, for example mtdev_has_mt_event(mtdev, ABS_MT_SLOT),
when I used 3 fingers to drag, geis got error XEvent type 84 in _x11_fd_callback function.

I argued that it might be xf86-input-synaptics-1.7.3`s issue, because geis backend
only received XEvent, then classified the gesture, but synaptics post the
multitouch event by xf86PostTouchEvent, in xf86-input-synaptics=1.7.3,
src/synaptics.c, about the line 2710,
http://cgit.freedesktop.org/xorg/driver/xf86-input-synaptics/tree/src/synaptics.c?h=synaptics-1.7-branch#n2710

And why ubuntu phone with multitouch touchscreen works well? It is based on Mir, utouch-geis,
sort of gesture recognition utils, is not it? or it is android-based, different from Linux multitouch protocol?
https://www.kernel.org/doc/Documentation/input/multi-touch-protocol.txt

please someone give me some advice, thanks a lot!