Print layers drifting towards rear

[cliffyk]

Another question I have is does your system on the first print layer move down to zero and then raise up a few mm before moving back down to perform the first print layer?

Yes, it moves down to a position "1 layer thickness" above the limit switch controlled zero. If a logical "zero" position has been set (using the Z=0 function) it will move the a position "1 layer thickness" above the logical "zero"...