Tool change gcode not reading current tool properly  

Tool change gcode not reading current tool properly

I'm trying to get my dual extruder printer to park properly when changing tools, so I added

G0 X{if current_extruder == 0}-40{else}435{endif} F15000

to the tool change gcode section in Prusa Slicer. If I start a print with T0, the whole print goes fine, each tool parks in the right spot during layer changes. If I start the print with T1, it tries to park T0 at 435, which just doesn't work. The gcode file has

G0 X435 F15000
T1

even though my start gcode is

G28 ;Home
T0
M109 T0 S[first_layer_temperature_0]
M109 T1 S[first_layer_temperature_1]
M605 S0 ;Disable broken builtin tool change parking
G1 Z15.0 F6000 ;Move the platform down 15mm
M84 S0 ;Disable idle hold timeout
;Prime the extruder
G92 E0
G1 F200 E3
G92 E0

so it should be reading T0 as the currently selected tool. It seems to be reading the tool it's going to change to as the current tool. Is there something I'm doing wrong?