Comment 36 for bug 1315360

I spoke with Andrew Duggan and he figured out that as of kernel 4.0 the touchpad is incorrectly detected as a clickpad. That's why the touchpad works, but in a flaky way. The good news is that this seems solvable. All you have to do is:

synclient ClickPad=0

Palm detection is also off by default and I find it basically unusuable without it, so also do:

synclient PalmDetect=1

These changes aren't saved after a reboot, but to make them permanent, create a configuration file in /usr/share/X11/xorg.conf.d/. You can do it with this one-liner:

echo -e "Section \"InputClass\"\n\tIdentifier \"touchpad catchall\"\n\tDriver \"synaptics\"\n\tMatchIsTouchpad \"on\"\n\tMatchDevicePath \"/dev/input/event*\"\n\n\tOption \"PalmDetect\" \"1\"\n\tOption \"ClickPad\" \"0\"\nEndSection" | sudo tee /usr/share/X11/xorg.conf.d/60-synaptics-options.conf &> /dev/null

So to summarize, we can get 100% touchpad functionality by installing Linux kernel >= 4.0, then running both
synclient ClickPad=0
synclient PalmDetect=1

Not sure who to go to to correct this default misconfiguration, but at least we can get everything working!