I have exactly the same problem, but only when It wakes from sleep.
I mean, it is using voodooPS2mouse.kext instead, because the driver is not loaded properly, due to the synaptic trackpad is recognized as ALPS. The behaviour is pretty good (having into account that is working with voodooPS2mouse instead voodooPS2trackpad), but when it wakes from sleep, there is an erratic movement from trackpad and I have the following in the kernel.log:
- ApplePS2mouse: unexpected data received from PS2 controller.
- ApplePS2controller: timed out on mouse input stream.
Someone could take a look on it.
By the way my trackpad is a Synaptic (ID: SYN0166, ID COMPATIBLES: SYN0100, SYN0002, PNP0F13).
The computer is a 8540w.