The tenant has been paying rent since, for all we know, five years ago.  That's why I wrote that this is considered a refund or rebate, only to the extent of the amount paid under the terms of the lease that is being terminated by the landlord.  The lease is property.   The tenant's basis in it is the amount already paid.  

Tenant:  "I will pay you $12,000 for the right to use your property for a year."

Landlord, ten months later:  "You have already paid me $10,000 but now I must ask you to leave, so I am returning $3,000 to you if you surrender your right to stay another two months.  And you won't have to pay the remaining $2,000 of the purchase price."

And comparing this to "cash for keys" is like comparing apples to turnips.  "Cash for keys" payments were made to people who no longer had an interest in the property, because it had been foreclosed.  They no longer owned a capital asset, so they could not have any basis to recover.