In Ubuntu 15.04, simply moving the mouse via touchpad scrolls the window

Blacklisting the psmouse improves the situation but xchat gnome is still having issues.

I followed instructions on https://github.com/mpalourdio/xps13

Check that your BIOS is version A03 or later, and touchpad firmware is up to date Touchpad firmware A00.

blacklist psmouse driver so that the trackpad uses i2c instead. Make sure there is no PS/2 in the output of xinput -list.

I noticed that xchat-gnome seems to be ignoring the touch-to-click setting and some other applications too (like VLC, but only the preference window).

In Xorg.log I see this error when the touchpad goes nuts:

(EE) [dix] DLL0665:01 06CB:76AD UNKNOWN: unable to find touch point 0

The only way I have to solve temporarily the issue is to disable the trackpad completely from the Settings panel and enable it again. Make sure you have an external mouse attached.