G-code or firmware bug on Wanhao Duplicator i3 Plus

firmware_bug.gcode

; NOTE: hotend must be preheated otherwise extruder retract is ignored!

; Monoprice Maker Select Plus/Wanhao Duplicator i3 Plus
; =========================================================
; An extruder retract in relative positioning causes
;   the X axis to no longer be able to home.
; Disabling the motors fixes the bug.


M117 Homing and moving to known position
G90                     ; Absolute positioning
G28 X0 Y0 Z0            ; Homing X, Y, and Z
G1 X30 Y30 Z30 F3000    ; Known position
M400                    ; Wait for move
M114                    ; Report position
G4 P1000                ; Pause

M117 Triggering bug
G91                     ; Relative positioning
G1 E-1 F300             ; Extruder retract 1mm, this sets up the bug
                        ; Both retraction/extrusion can trigger the bug
M400                    ; Wait for current moves to finish
M114                    ; Report position
G4 P1000                ; Pause

M117 Homing X and Y (1 of 3)
G90                     ; Absolute positioning
G28 X0 Y0               ; Homing X and Y
                        ; Due to bug, only Y homes but X moves a bit
M400                    ; Wait for current moves to finish
M114                    ; Report position
G4 P1000                ; Pause

M117 Homing X and Y (2 of 3)
G90
G28 X0 Y0
M400
M114
G4 P1000

M117 Homing X and Y (3 of 3)
G90
G28 X0 Y0
M400
M114
G4 P1000

; Maybe moving X and Y will cause X to realize it's no longer home?
M117 Moving X and Y
G90                     ; Absolute positioning
G1 X20 Y20 F3000        ; Moving X and Y
M400
M114
G4 P1000

M117 Homing X and Y
G90
G28 X0 Y0               ; Nope, Y homes, but X still doesn't
M400
M114
G4 P1000

M117 Fixing bug by disabling motors
M18                     ; Disable motors
M114                    ; Report position
G4 P1000                ; Pause

M117 Homing X and Y
G90                     ; Absolute positioning
G28 X0 Y0               ; Homing X and Y, actually works this time
M400                    ; Wait for current moves to finish
M114                    ; Report position


; We're done here, let the motors rest
M18