According to an official of the Ukrainian Foreign Ministry, the relations between Ukraine and Romania are still marred by the issue of dual citizenship.
In line with Romanian law, Ukrainian citizens who lost Romanian citizenship involuntarily (including descendants) may have their Romanian citizenship restored without having to take up residence in Romania or to renounce Ukrainian citizenship. This rule has effects especially in those border regions that have once been part of the Romanian state.
Ukraine does not accept dual citizenship and has often criticised Romanian policy. Despite a recent revival of friendly relations between the two countries, the issue of citizenship remains a major problem. In the eyes of the Ukrainian official, the distribution of Romanian passports to Ukrainian citizens amounts to “an unfriendly step” towards Ukraine.
The Romanian Foreign Ministry reacted to these declarations by assuring that Romania does not pursue a policy of restoration of citizenship en masse or based on ethnic grounds. The Ministry added that not all those who regain Romanian citizenship apply for a Romanian passport.

Read an article with the position of the Ukrainian official
Read an article with the response by Romanian Foreign Ministry

See also the EUDO Citizenship Country Reports on Romania and Ukraine.