Can you support your statement by providing any links to the official documents? I know that the Ukrainian Parliament indeed approved in the first reading the bill that would require to notify the government upon obtaining foreign citizenship, but it has to be approved in the second reading and then signed by the President to become an actual law. As of right now, there is no such law, as far as I know.
Also, renouncing Ukrainian citizenship is a very lengthy and cumbersome process because you are required to gather so many bureaucratic papers (some of them only from Ukraine) that you will probably give up in the initial stages. I was thinking to renounce Ukrainian citizenship to be able to obtain security clearance, but after researching into it I understood that it was not worth the time I would have to spend. Also, the Ukrainian consulate will not serve you if you show them your US passport, but you need some of their service if you want to initiate the renunciation, so it is a catch 22.
As far as travelling to Ukraine on Ukrainian passport, it is perfectly legal because you are considered a Ukrainian citizen until the President signs a decree that strips you of citizenship. The President will not issue such decree if you do not submit the renunciation form first. I know many Ukrainian people who travel to Ukraine on Ukrainian passports and no one had any problems. Some of them choose to travel on US passports - which is illegal under Ukrainian law - yet they also have no problems because border guards do not want to bother with them.