Rsync disconnects my external USB drive

I read through a number of posts on here and the benefits of Rsync keeping mirror copies without having to perform entire backups. That's a good thing if you have terabytes of data to backup and therefore a big time saver on incremental updates. So as suggested on a number of posts, I initially ran a standard backup job using Frontview so I could get my full backup for each share to my external USB drive. I then changed it to use Rsync where my source was the NAS and path was the external USB path/folder. The destination was changed to be the NAS local share. I hit go on the job and it runs and completes quickly seeing there are no differences between the source & destination at this time. I then drop a small text file into the NAS share like I always do when backing up my files. I then proceed to hit go on the backup job and it completes without any issues. HOWEVER, it results in my text file being deleted from the NAS share rather than mirroring over to the external USB drive. This is actually the opposite of what I expected. I further confirmed it by placing the text file on the external USB HD folder and re-run the job. The logs show it copies the file over to the NAS. The reverse is true and deleting the file from the USB HD folder and re-running the job shows the file is removed from the NAS.

So, I figure changing the path under the source to be the local NAS share and the destination to be the USB drive path/folder would do the trick. Note: Rsync is still the protocol being used here. Anyhow, retesting does show it works as I would think. So placing a file on the NAS share and re-running the job shows it is copied over to the external HD folder. Unfortunately, the the USB drive is disconnected/unmounted when the job completes. I have to recycle the USB drive or unplug the USB cable and plug it back in for the NAS to see it. Again, the job does complete correctly but for some reason it disconnects the USB drive.

Is this normal and the way the client/server functions work for Rsync? I would say most of the posts on this forum and otherwise are written using Rsync between two NAS which may be its intended purpose. For the time being, I have reverted back to using the built in backup job function. Otherwise, my first job would turn off the USB drive and result in subsequent jobs failing.

I'm thinking this is a bug but hoping someone else can confirm it either way.