I’ve found a strange bug. I have a project with lots of mockups. At one point I wanted to duplicate few mockups, but in the context menu after selecting several mockups it was not possible (the option “duplicate” was disabled). So I thought, what if ALT+Drag (like with widgets) could do that for me? I tried that, and then my selected mockups were gone. It turned out to be that they were removed only from the nativation panel. First I thought, they were deleted. However, it is possible to insert links to those invisible mockups and to open and edit them using links. When I export mockups to PDF, those invisible mockups are also in the list of all mockups.
It’s a bit confusing…
P.S. maybe as a feature request, it would be nice to have a possibility to duplicate several mockups at a time, and not just one at a time