In another of my nitpicky observations about OMV...
When running a backup via USB Backup -> Run, a Modal dialog is opened which can not be closed until the backup is completed. This can take hours.
If possible, a better design might be to add the backup to a run queue and return control of the dialog back to the user.
If this seems sane I'll open a bug. But before doing that I wanted to get developer feedback on why and how they made their design decisions.