Yep, I think this is basically the problem with this post, it's Dropbox with an open source client and maybe that is what he doesn't want it to be.
Delete that file on one device, it is gone from all that share it.
Scripts can copy out from the Dropbox to both negate your issue and proliferate backup copies to many physical locations.
Especially with Packrat feature.
I'm quite aware of what tarsnap is.
* Mobile support
* Windows support
* A web interface
* Any way of using it other than CLI
TFA left all that stuff in place. "tarsnap the software" does not change at all.