foreign_unique without foreign_selector doesn't work
The reason is a wrong value delivered by JSON concerning uniqueness/selector.
Use the IRRE Testsuite from http://inpublica.de/typo3/T3X_irre_testsuite.t3x, create new company and person records of type "[IRRE Foreign Field Attributes] ..." and then try to relate companies to persons by using the select field of the child records.
This issue was reported by Thomas Murphy on the irre-list, see http://lists.typo3.org/pipermail/typo3-project-irre/2007-February/000020.html
(issue imported from #M5098)