diff --git a/scss/components/form/_transfer.scss b/scss/components/form/_transfer.scss
index 10b1381d..49a5468c 100644
--- a/scss/components/form/_transfer.scss
+++ b/scss/components/form/_transfer.scss
@@ -42,7 +42,7 @@
   &-select > &-checkboxes,
   &-result > &-selections {
     flex-grow: 1;
-    height: 0;
+    max-height: 100%;
     overflow: auto;
   }
 
@@ -145,7 +145,7 @@
 
           > .#{$ns}Transfer-checkboxes {
             flex-grow: 1;
-            height: 0;
+            max-height: 100%;
             overflow: auto;
           }
         }
diff --git a/src/components/TreeCheckboxes.tsx b/src/components/TreeCheckboxes.tsx
index e267d612..aba70da0 100644
--- a/src/components/TreeCheckboxes.tsx
+++ b/src/components/TreeCheckboxes.tsx
@@ -78,6 +78,9 @@ export class TreeCheckboxes extends Checkboxes<
 
     if (option.disabled) {
       return;
+    } else if (option.defer && !option.loaded) {
+      onDeferLoad?.(option);
+      return;
     }
 
     let valueArray = Checkboxes.value2array(value, options, option2value);