Steps to reproduce

1. Create a (page) dialog with a jcrMulti(Value)Field
2. Add another field as it's child e.g. linkField
3. Add a validator to the linkField
4. Enter content that does not match the validator 
5. No error is shown, but the form won't submit (atleast that's good)

Expected results

We expect to see an error message just like other field that are not directly below a multifield

Actual results

No error is shown

Workaround

n/a

Field configuration: 

 products:
      $type: jcrMultiValueField
      required: true
      field:
        $type: linkField
        textInputAllowed: true
        filteringMode: CONTAINS
        showOptions: true
        required: true
        datasource:
          $type: jcrDatasource
          workspace: products
          describeByProperty: displayName
          allowedNodeTypes:
            - client:productCategory
            - client:productLine
            - client:decorSet
            - client:decor
            - client:finish
        validators:
          requiresCategory:
            $type: nodePropertyValidator
            propertyName: jcr:primaryType
            pattern: ^client:finish$
            errorMessage: validators.requiresNodeType.errorMessage
 

 Custom validator used:

The custom validator used is attached, feel free to add it to the product if it satisfies needs. 
But it's not needed to reproduce the issue, (required also fails). 
The reason we're using the custom validator is to make sure the chooser shows the content tree completely to preserve the tree structure, but we only allow the deepest level (finish in this case).