If the option DISABLE_INACTIVE_EXTRUDER ist active the extruder switch to early to inactive because there are some moves in the buffer. So the planner wait 32 moves to disable the unused extruder.

Marlin/planner.cpp

@@ -96,6 +96,8 @@ float autotemp_factor=0.1;
 bool autotemp_enabled=false;
 #endif
 
+unsigned char g_uc_extruder_last_move[3] = {0,0,0};
+
 //===========================================================================
 //=================semi-private variables, used in inline  functions    =====
 //===========================================================================
@@ -662,11 +664,34 @@ block->steps_y = labs((target[X_AXIS]-position[X_AXIS]) - (target[Y_AXIS]-positi
   {
     if (DISABLE_INACTIVE_EXTRUDER) //enable only selected extruder
     {
+
+      if(g_uc_extruder_last_move[0] > 0) g_uc_extruder_last_move[0]--;
+      if(g_uc_extruder_last_move[1] > 0) g_uc_extruder_last_move[1]--;
+      if(g_uc_extruder_last_move[2] > 0) g_uc_extruder_last_move[2]--;
+      
       switch(extruder)
       {
-        case 0: enable_e0(); disable_e1(); disable_e2(); break;
-        case 1: disable_e0(); enable_e1(); disable_e2(); break;
-        case 2: disable_e0(); disable_e1(); enable_e2(); break;
+        case 0: 
+          enable_e0(); 
+          g_uc_extruder_last_move[0] = BLOCK_BUFFER_SIZE*2;
+          
+          if(g_uc_extruder_last_move[1] == 0) disable_e1(); 
+          if(g_uc_extruder_last_move[2] == 0) disable_e2(); 
+        break;
+        case 1:
+          enable_e1(); 
+          g_uc_extruder_last_move[1] = BLOCK_BUFFER_SIZE*2;
+          
+          if(g_uc_extruder_last_move[0] == 0) disable_e0(); 
+          if(g_uc_extruder_last_move[2] == 0) disable_e2(); 
+        break;
+        case 2:
+          enable_e2(); 
+          g_uc_extruder_last_move[2] = BLOCK_BUFFER_SIZE*2;
+          
+          if(g_uc_extruder_last_move[0] == 0) disable_e0(); 
+          if(g_uc_extruder_last_move[1] == 0) disable_e1(); 
+        break;        
       }
     }
     else //enable all