TYPO3 Core

There is a problem with the TCA type="group" when a new records is created and there are already saved relations in the database.
All existing relations from the mm tables are automatically added to the items field.

I found the problem while using sys_categroy, if there are already existing category-relations in the database.

1. create sy_category
2. create any random data (tt_content, news,...) and add a category relation to that.
3. create a new sys_category -> items are prefilled with the data in the sys_category_relation_mm

The problem is, that the new data has no numeric UID and in the RelationHandler->readMM class the where clause is only set for the uid, if it is an integer (MathUtility::canBeInterpretedAsInteger($uid)).