Muy buena pregunta.
Es el comportamiento normal que queden anidadas, así ocupan menos espacio.
Snpashots no son backups:
https://forums.virtualbox.org/viewtopic.php?f=35&t=84332Creo que cuando borras una de por en medio te avisa:
Deleting the snapshot will cause the state information saved in it to be lost, and storage data spread over several image files that VirtualBox has created together with the snapshot will be merged into one file. This can be a lengthy process, and the information in the snapshot cannot be recovered.
Are you sure you want to delete the selected snapshot ?