Do not use feedrate multiiply on Z and E only moves.

Marlin/Marlin.pde

@@ -1603,7 +1603,13 @@ void prepare_move()
   clamp_to_software_endstops(destination);
 
   previous_millis_cmd = millis(); 
-  plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate*feedmultiply/60/100.0, active_extruder);
+  // Do not use feedmultiply for E or Z only moves
+  if( (current_position[X_AXIS] == destination [X_AXIS]) && (current_position[Y_AXIS] == destination [Y_AXIS])) {
+      plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate/60, active_extruder);
+  }
+  else {
+    plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate*feedmultiply/60/100.0, active_extruder);
+  }
   for(int8_t i=0; i < NUM_AXIS; i++) {
     current_position[i] = destination[i];
   }