I had a warehouse rented in Moria with nothing in it anymore. The payment upkeep ticked over, and it locked (as I had no NCC due to trades, not my main currency). I attempted to cancel it, but it won’t let me due to incomplete payment (that could be a feature request.)
However, just on a whim, I clicked ‘Rent Unit’, mostly expecting it to fail. Instead, it rented another unit, locked it immediately, and ‘refunded’ me 40 NCC.
Being confused, and making sure I read it right, I clicked ‘rent unit’ a second time, and the exact same thing played out again. I now have 3 locked units, and 86 NCC total.