This is currently, from what I've learned atleast, not possible without the clips getting alinged wrong and the playhead jumping around. This is how I would do it now:
- Start transport
- Mark a part
- Ctrl+c and then ctrl+shift+v to insert a duplication
Try that and you will see my issue =). Easily solved by making duplicate part/clip done by for example ctrl+mouse drag, like shift+mouse drag is copy part right now.