Adding nominees to more then one election
If you then open and save the first election without changing anything, new entries in the MM-Table tx_election_domain_model_election are created. Seems like an extbase error or some missing/strange configuration. MM-Configuration is in ext_typoscript_setup.txt.
In this test data set voting-4electors.sql.gz only the first election has nominees assigned. Open the second election and assign a nominee to see the effect.
Similar places where this error could happen are the opposite site of the election-nominee-relation and the electorate-elector-relation and it's opposite site.