nophead, this is what the file generated says - that first Z entry is looks fine to me, thought I'm not a gcode expert, but it continues to lift.
; generated by Slic3r 0.8.4 on 2012-07-04 at 22:29:57
; layer_height = 0.3
; perimeters = 2
; solid_layers = 3
; fill_density = 0.4
; nozzle_diameter = 0.5
; filament_diameter = 3
; extrusion_multiplier = 1
; perimeter_speed = 65
; infill_speed = 80
; travel_speed = 100
; scale = 1
; single wall width = 0.70mm
M104 S200 ; set temperature
G28 ; home all axes
M92 E281; calibrate E
M109 S200 ; wait for temperature to be reached
G90 ; use absolute coordinates
G21 ; set units to millimeters
G92 E0 ; reset extrusion distance
M82 ; use absolute distances for extrusion
G1 Z0.300 F6000.000