🐛 Fix IDEX + DISABLE_INACTIVE_EXTRUDER (#22925)

Marlin/src/module/motion.cpp

@@ -1193,6 +1193,7 @@ FORCE_INLINE void segment_idle(millis_t &next_idle_ms) {
         case DXC_MIRRORED_MODE:
         case DXC_DUPLICATION_MODE:
           if (active_extruder == 0) {
+            set_duplication_enabled(false); // Clear stale duplication state
             // Restore planner to parked head (T1) X position
             float x0_pos = current_position.x;
             xyze_pos_t pos_now = current_position;

Marlin/src/module/planner.cpp

@@ -2207,23 +2207,23 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
 
       #if ENABLED(DISABLE_INACTIVE_EXTRUDER) // Enable only the selected extruder
 
+        // Count down all steppers that were recently moved
         LOOP_L_N(i, E_STEPPERS)
           if (g_uc_extruder_last_move[i]) g_uc_extruder_last_move[i]--;
 
+        // Switching Extruder uses one E stepper motor per two nozzles
         #define E_STEPPER_INDEX(E) TERN(SWITCHING_EXTRUDER, (E) / 2, E)
 
+        // Enable all (i.e., both) E steppers for IDEX-style duplication, but only active E steppers for multi-nozzle (i.e., single wide X carriage) duplication
+        #define _IS_DUPE(N) TERN0(HAS_DUPLICATION_MODE, (extruder_duplication_enabled && TERN1(MULTI_NOZZLE_DUPLICATION, TEST(duplication_e_mask, N))))
+
         #define ENABLE_ONE_E(N) do{ \
-          if (E_STEPPER_INDEX(extruder) == N) { \
-            stepper.ENABLE_EXTRUDER(N); \
-            g_uc_extruder_last_move[N] = (BLOCK_BUFFER_SIZE) * 2; \
-            if ((N) == 0 && TERN0(HAS_DUPLICATION_MODE, extruder_duplication_enabled)) \
-              stepper.ENABLE_EXTRUDER(1); \
-          } \
-          else if (!g_uc_extruder_last_move[N]) { \
-            stepper.DISABLE_EXTRUDER(N); \
-            if ((N) == 0 && TERN0(HAS_DUPLICATION_MODE, extruder_duplication_enabled)) \
-              stepper.DISABLE_EXTRUDER(1); \
+          if (N == E_STEPPER_INDEX(extruder) || _IS_DUPE(N)) {    /* N is 'extruder', or N is duplicating */ \
+            stepper.ENABLE_EXTRUDER(N);                           /* Enable the relevant E stepper... */ \
+            g_uc_extruder_last_move[N] = (BLOCK_BUFFER_SIZE) * 2; /* ...and reset its counter */ \
           } \
+          else if (!g_uc_extruder_last_move[N])                   /* Counter expired since last E stepper enable */ \
+            stepper.DISABLE_EXTRUDER(N);                          /* Disable the E stepper */ \
         }while(0);
 
       #else