Lists with more than 1,000 leads will not be cloned.

[Caryl_Mostacho]

Has anyone ever gotten that warning when you're cloning a program? 

[Anonymous]

We do this because copying the list membership can be slow and is rarely what users seem to want. We still copy the list, but we don't copy the members. If you need the membership, you can run a campaign or a flow action to add the leads to the new list.