Romanians were also called to vote for a referendum when voting for EU Parliament elections in 2019. However, the organizing for diaspora voting was very problematic and many could not vote at all:
An impressive number of Romanians living and working abroad have come to polls on Sunday to vote at the European elections and at the referendum for justice. Unfortunately, the polling stations were insufficient, and problems were also encountered on the scarce voting stamps, ballot papers or boxes, so that a considerable amount of people did not manage to cast their votes.
I cannot find a source now, but the Foreign Ministry also blamed the referendum for putting extra pressure on the voting polls.
From my perspective "piggyback" (organizing in the same time) a referendum sounds like a great idea since it reduces the costs and also might motivate the voters (they come if they wish to vote for at least one of the elections). However, I am wondering if this practice is heavily used across EU or it rarely happens so.
Question: Is organizing "piggybacked" referendums something unusual in EU? By EU I mean any European Union country.