Rental payments are split between payment of imputed interest and liability. The current liability is the portion of the total liability that will be paid in the next 12 months. In other words, it's the difference between the liability now and what the liability will be 12 months from now. It is a negative number, to indicate a credit. All liability amounts are discounted numbers.
On some occasions, the current liability is zero. This indicates a negative principal amortization lease; the rent paid in a period is less than the interest accrued. It is most common on long leases with substantial rent increases. In such a case, the interest is added back to the liability, to be paid at a future date. The current liability becomes non-zero when the liability paid in the next 12 months is greater than the interest being added to the liability.