Comment 214 for bug 296167

synaptics puts a grab on the device, so the "grab failed" message will happen for any device using synaptics. For normal mice it should succeed though.

There's another thing that you could try: add Option AutoAddDevices "off" to the ServerLayout This will force the mouse driver to load. If you can reproduce the problems with the mouse driver as well, that means it's either the X server, or the kernel. If not, then it's the driver. However, since Robert doesn't have a touchpad but sees the same issues, it doubt it's the driver.