Only clear the receivers when the UI is actually being closed

Author: Zorbatron

src/main/java/gregtech/api/mui/GregTechGuiScreen.java

@@ -1,6 +1,7 @@
 package gregtech.api.mui;
 
 import gregtech.api.GTValues;
+import gregtech.client.ClientProxy;
 import gregtech.integration.jei.JustEnoughItemsModule;
 
 import net.minecraftforge.fml.relauncher.Side;
@@ -48,7 +49,11 @@ public GregTechGuiScreen(String owner, ModularPanel mainPanel, String themeId) {
 
     @Override
     public void onClose() {
-        registeredRecipeTransferReceivers.clear();
+        // Only clear all registered recipe receivers when the UI is truly closing, ie not just opening JEI over it.
+        if (ClientProxy.isGUIClosingPermanently) {
+            // Clear all registered recipe receivers on UI close, just in case.
+            registeredRecipeTransferReceivers.clear();
+        }
     }
 
     @Override

src/main/java/gregtech/api/mui/sync/RecipeTransferSyncHandler.java

@@ -28,6 +28,7 @@ protected int getTransferHandlerPriority() {
         return 0;
     }
 
+    // TODO: this method is never actually called. Either fix on our side or wait for it to get fixed in MUI.
     @ApiStatus.OverrideOnly
     @MustBeInvokedByOverriders
     @Override

src/main/java/gregtech/client/ClientProxy.java

@@ -57,6 +57,7 @@
 import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.util.text.TextFormatting;
 import net.minecraftforge.client.GuiIngameForge;
+import net.minecraftforge.client.event.GuiOpenEvent;
 import net.minecraftforge.client.event.ModelBakeEvent;
 import net.minecraftforge.client.event.ModelRegistryEvent;
 import net.minecraftforge.client.event.MouseEvent;
@@ -86,6 +87,8 @@
 @Mod.EventBusSubscriber(Side.CLIENT)
 public class ClientProxy extends CommonProxy {
 
+    public static boolean isGUIClosingPermanently = false;
+
     public void onPreLoad() {
         super.onPreLoad();
 
@@ -428,4 +431,9 @@ private static void renderToolbeltHotbar(GuiIngameForge gui, ItemStack stack, It
             GlStateManager.disableBlend();
         }
     }
+
+    @SubscribeEvent
+    public static void onGuiChange(GuiOpenEvent event) {
+        isGUIClosingPermanently = (event.getGui() == null);
+    }
 }