Scheduled clonings start one behind

Thank you for this wonderful plugin!
On my network, I want logged-in users to be able to create their own clones of a template site from a custom front-end. Following your page on how to trigger NS Cloner via PHP from another plugin, I decided to rely on the indirect/scheduled method through ns_cloner()->schedule->add(), as I cannot exclude the possibility of one user starting a new cloning process while another is not yet finished. Since I pass time() as the second argument, I was expecting a queued, yet immediate processing.
This works like a charm when cloning one site at a time. But when I add two or more cloning jobs quickly after one another the Cloner only adds them to the schedule (they will show in the NS Cloner admin panel) but stops cloning after the first job. Quite strangely, it would then only continue with the next scheduled task when I add another one – which will then again not be executed until I add more…
Effectively, it gives me that weird “cloning one-behind” experience suggested in the title: Scheduling clone jobs A and B causes cloning of A, adding C causes cloning of B, and so on.
Is there anything I can do about it, or is this just a bug in the Cloner?
Thanks in advance!