Looks like the tool switch code tries to move the printer in cartesian space not delta... Commenting out the plan_set_position() and prepareMove() shown below fixes this for me.
else if(code_seen('T'))
{
tmp_extruder = code_value();
if(tmp_extruder >= EXTRUDERS) {
SERIAL_ECHO_START;
SERIAL_ECHO("T");
SERIAL_ECHO(tmp_extruder);
SERIAL_ECHOLN(MSG_INVALID_EXTRUDER);
}
else {
boolean make_move = false;
if(code_seen('F')) {
make_move = true;
next_feedrate = code_value();
if(next_feedrate > 0.0) {
feedrate = next_feedrate;
}
}
#if EXTRUDERS > 1
if(tmp_extruder != active_extruder) {
// Save current position to return to after applying extruder offset
memcpy(destination, current_position, sizeof(destination));
#ifdef DUAL_X_CARRIAGE
// [removed from post because long and not relevant]
#else
// Offset extruder (only by XY)
int i;
for(i = 0; i < 2; i++) {
current_position = current_position -
extruder_offset[active_extruder] +
extruder_offset[tmp_extruder];
}
// Set the new active extruder and position
active_extruder = tmp_extruder;
#endif //else DUAL_X_CARRIAGE
// this part doesn't work on a delta. current_position is in cartesian space, not delta
plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
// Move to the old position if 'F' was in the parameters
if(make_move && Stopped == false) {
prepare_move();
}
}
#endif
SERIAL_ECHO_START;
SERIAL_ECHO(MSG_ACTIVE_EXTRUDER);
SERIAL_PROTOCOLLN((int)active_extruder);
}
}