TYPO3 Core

Given a form object with a property which may contain a list of objects (array/ObjectStorage) as well as a list of checkboxes built from all available objects for that property:

<f:form object="{object}" name="object">
  <f:for each="{availableObjects}" as="availableObject">
    <f:form.checkbox
      property="foo" 
      value="{availableObject}" 
      multiple="1"/>
  </f:for>
</f:form>

If you select one of the options, the checked attribute is not properly set on the subsequent form display. This is due to the fact that the CheckboxViewHelper converts the incoming value for the value attribute to an identifier through AbstractFormFieldViewHelper::getValue() but does not do the same for the property value. Thus e.g. an UID like 42 is searched in an array of objects which will never succeed. (Source)

A possible fix is to run PersistenceManager->getIdentifierByObject on each value within property too, thus comparing e.g. an UID with an array of UIDs. This is the same what AbstractFormFieldViewHelper::getValue() does when $convertObjects is set to TRUE (default).