Ekko Ult

I just did some tests with some friends and found some interesting things when playing Ekko if Zed uses Death Mark and Ekko were to use his ult after it was applied the Death Marl will not stay on him. But if Karthus were use Requiem and Ekko tries to dodge/remove it with his ult it would not work and the Requiem is still applied and will do damage to Ekko. Also if Varus uses his Chain of Corruption on an enemy champ and Ekko also is linked in the chain and tries to avoid being stunned or be removed from the link will not remove it and he will still be stunned. Tell me if you have the same or different experiences maybe when playing Karthus and Varus I may have miss timed using Ekko's Ult and would like to know if I did or is this is how the ult is suppose to work.