I noticed this in UM half a year ago. I assume it relates to all versions of Ubuntu MATE and probably Debian. The package unattended-upgrades depends on the software-properties package which I assume is not safe to uninstall.
unattended-upgrades has not caused me problems, but it's a potential trouble-maker (think Windows 10) so it would be nice if it didn't come with unnecessary dependencies.
This package has been installed for a while, but it being installed doesn’t mean the programs it contains ever run.
I don’t think the dependency is unnecessary since without that package installed, a feature of Software Properties would break.
What’s problematic since Xenial is that the default option in software properties for security updates has been changed to “Download and install automatically”, which is a change I object to. Now of course nothing prevents individual users from changing that option back to the “Display Immediately” that it used to be.
Thanks for filing a bug report about this. It’s somewhat troubling to see that noone has acknowledged your bug report and this is something that affects all Ubuntu flavours.
One might say that this is a minor bug, but I don’t think so. With the unattended-upgrades package in place Ubuntu has a mechanism to deliver updates in the background. This is very troublesome as I see it.
Your bug report is great, but the silence around it is not so great…
Thanks anyway @ouroumov 
Hallo
I wondered why that was happening but didn’t take the time to look into it. Thanks for pointing it out.