If you launch simple-touch, zoom in using <meta>+<mouse scroll>, then touch simple-touch you can observe that the coordinates touched in simple touch are off by the amount that one is zoomed in.
Observed on 1.2.1 and on master (c4df4082c24ab430d1f91970302702e6078221f3)
I've posted a patch for this on the mailing list:
Author: Neil Roberts <email@example.com>
Date: Thu May 1 16:13:55 2014 +0100
Take into account the zoom when applying the output transform
When converting output-relative coordinates (such as from an input
event) to global coordinates it now takes into account the zoom
transform. Previously this would only work for the primary pointer
because the transform doesn't affect the primary pointer position due
to that way zoom follows the mouse. Touch events and multiple pointers
were not working correctly.