No warning about decay when forgetting to add a system to "lands"

[se5a]

I've just lost a whole city and had another half decay with no warning, just poof, city no longer exists.
only indication that it was happening was that a city that was mining high quality oil suddenly stopped existing.
I thought it was due to a rollback. 

Only way I figured out what was happening was because I scrolled through the history reports in the second city in that system, and found a couple of older ones which mentioned decay, I had thought that I had already added this system to my lands, but checking the lands tab in my bio it didn't show.