[TYPO3-mvc] Problem with ObjectStorageConverter (Rewritten Property Mapper)

[Kai Tallafus]

Dear List,

I have a domain model using an ObjectStorage for a 1:n relation to another model. In Frontend I have a form using a multiselect field for editing this ObjectStorage. 

I´m using extbase/fluid version 4.7.4. This works fine, until I edit a model, which has existing relations and I deselect ALL relations. When submitting the form, the ObjectStorage will not get updated.

I tried to track this down and discovered the following:
The method Tx_Extbase_Property_TypeConverter_ObjectStorageConverter::convertFrom() will create a new ObjectStorage and attach() all converted child properties to it. The attach() method will set the isModified property to TRUE, so it is correctly recognized as "dirty" as long as the new ObjectStorage is not empty. But if it´s empty, the attach() method will never be called, so the Storage will not be marked as modified and therefore will not be updated.

Can someone confirm this problem or at least tell me if I´m doing something wrong?

Thanks and regards,
Kai