Stamina will be set to full if Stamina is disabled.

src/main/java/emu/grasscutter/game/managers/StaminaManager/StaminaManager.java

@@ -190,7 +190,9 @@ public class StaminaManager {
 
     // Returns new stamina and sends PlayerPropNotify
     public int setStamina(GameSession session, String reason, int newStamina) {
-        if (Grasscutter.getConfig().OpenStamina) {
+        if (!Grasscutter.getConfig().OpenStamina) {
+            newStamina = player.getProperty(PlayerProperty.PROP_MAX_STAMINA);
+        }
         // set stamina
         player.setProperty(PlayerProperty.PROP_CUR_PERSIST_STAMINA, newStamina);
         session.send(new PacketPlayerPropNotify(player, PlayerProperty.PROP_CUR_PERSIST_STAMINA));
@@ -200,8 +202,6 @@ public class StaminaManager {
         }
         return newStamina;
     }
-        return player.getProperty(PlayerProperty.PROP_CUR_PERSIST_STAMINA);
-    }
 
     // Kills avatar, removes entity and sends notification.
     // TODO: Probably move this to Avatar class? since other components may also need to kill avatar.