All I can say that for naturalized citizens it's an explicit betrayal of the oath they give when getting naturalized.Consider that some countries do not recognise any renunciation taken as part of a citizenship oath elsewhere; the UK, for example, says it's the only authority to grant or remove its citizenship and removal of UK citizenship, if I remember right, only follows conviction for treason, which hasn't happened since WW2.
I'm not talking law of other nations. They might still consider their citizens loyal to them. However, when naturalized citizen takes the oath in the US, he/she is supposed to make it in good faith and oath renounces loyalties to any foreign entity. Whether that entity recognizes it or not is irrelevant. It is not that entity that takes the oath.