Now, that's odd. I have several radials stapled down in my back yard, and they have never come up while mowing.
I learned THAT one the hard way a long, long time ago, when I lost the 80 meter radial to my (then) roof-mounted HF6V; I hadn't had it properly stapled to the ground, the mower got it, and I had a fun hour removing copper wire from around the mower blade axis.
I suspect that your landlord is afraid that that might happen, and is manually removing the radial(s).
One thing that can be done... find a flat-bladed shovel, cut a small slit in the grass (just enough to get under the thatch & roots), slip the radial(s) in under the grass. Within a week or so, the slit is completely gone. Of course, it's easier for me to do this, since I'm not renting, just payingblood moneya mortgage to the bank.