TYPO3 Exception 1481647089¶
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Nesting select and group elements in flex form sections is not allowed with MM relations¶
#1481647089: Invalid flex form data structure on field name "pi_flexform" with element "foo" in section container "content": Nesting select and group elements in flex form sections is not allowed with MM relations.
Happens on TYPO3 v8 when using a multiRelation field inside a section container