diff --git a/backend/models/subject.py b/backend/models/subject.py
index 16b06d1..62a3b47 100644
--- a/backend/models/subject.py
+++ b/backend/models/subject.py
@@ -71,18 +71,18 @@ class SubjectModel:
     
     @staticmethod
     async def has_related_data(subject_id: int) -> bool:
-        """检查科目是否有关联数据"""
-        return False
+        """检查科目是否有关联的作业数据"""
+        sql = "SELECT COUNT(*) AS cnt FROM assignments WHERE subject_id = %s"
+        result = await execute_one(sql, (subject_id,))
+        return result and result.get("cnt", 0) > 0
     
     @staticmethod
     async def delete(subject_id: int) -> bool:
-        """软删除科目（设置 is_active = 0），如果已禁用也返回成功"""
+        """真正删除科目记录"""
         subject = await SubjectModel.get_by_id(subject_id)
         if not subject:
             return False
-        if subject.get("is_active") == 0:
-            return True  # 已禁用，视为成功
-        sql = "UPDATE subjects SET is_active = 0 WHERE subject_id = %s"
+        sql = "DELETE FROM subjects WHERE subject_id = %s"
         result = await execute_update(sql, (subject_id,))
         return result > 0
     
diff --git a/backend/services/subject_service.py b/backend/services/subject_service.py
index 2ab56cd..7743050 100644
--- a/backend/services/subject_service.py
+++ b/backend/services/subject_service.py
@@ -67,7 +67,7 @@ class SubjectService:
     
     @staticmethod
     async def delete_subject(subject_id: int) -> Dict[str, Any]:
-        """删除科目（软删除）"""
+        """删除科目（真正删除记录）"""
         # 检查科目是否有关联数据
         has_data = await SubjectModel.has_related_data(subject_id)
         if has_data:
@@ -76,7 +76,7 @@ class SubjectService:
         result = await SubjectModel.delete(subject_id)
         
         if result:
-            logger.info(f"禁用科目: {subject_id}")
+            logger.info(f"删除科目: {subject_id}")
             return {"success": True}
         else:
-            return {"success": False, "message": "禁用科目失败"}
\ No newline at end of file
+            return {"success": False, "message": "删除科目失败"}
\ No newline at end of file
diff --git a/frontend/assets/css/style.css b/frontend/assets/css/style.css
index 9f336da..7a847d5 100644
--- a/frontend/assets/css/style.css
+++ b/frontend/assets/css/style.css
@@ -853,10 +853,6 @@ tr:hover {
 
 .action-dropdown-menu {
     display: none;
-    position: absolute;
-    bottom: 100%;
-    right: 0;
-    margin-bottom: 4px;
     background: white;
     border-radius: 8px;
     box-shadow: 0 4px 16px rgba(0, 0, 0, 0.12);
@@ -899,12 +895,6 @@ tr:hover {
     color: var(--color-danger-dark);
 }
 
-@media (max-width: 768px) {
-    .action-dropdown-menu {
-        right: auto;
-        left: 0;
-    }
-}
 
 /* ========== 链接 ========== */
 .link {
@@ -937,11 +927,11 @@ tr:hover {
     vertical-align: top;
 }
 
-/* 原因列：每行最少7个字，自动换行 */
-.history-reason {
+/* 原因列：每行最少7个字，自动换行（使用td前缀提升优先级，防止被preserve-newlines覆盖） */
+td.history-reason {
     min-width: 7em;
     max-width: 200px;
-    white-space: normal;
+    white-space: normal !important;
     word-break: break-word;
     line-height: 1.5;
     vertical-align: top;
diff --git a/frontend/assets/js/common.js b/frontend/assets/js/common.js
index d6c3e22..22321dd 100644
--- a/frontend/assets/js/common.js
+++ b/frontend/assets/js/common.js
@@ -359,6 +359,8 @@ function closeAllDropdowns() {
         m.style.position = '';
         m.style.left = '';
         m.style.top = '';
+        m.style.bottom = '';
+        m.style.right = '';
         m.style.transform = '';
         var toggle = m.closest('.action-dropdown');
         if (toggle) {