Makes no sense at all. What does the date that I pay have to do with anything? If you owe me $30 cash back, you jolly well use it to offset my next month's bill. What rubbish policy to hold the cashback because I paid first. Then are they encouraging people to pay late?
Actually, under clause 2.2 of the 'UOB ONE Credit Card Terms and Conditions',
"Quarterly Cash Rebates may only be used to settle Card Transactions incurred on a Principal Cardmember’s Card or his Supplementary Cardmember’s Card (if any), ..."
Strictly speaking, if there are no transactions to settle because everything has been paid, the Rebates should not appear.
And of course, every bank incorporates all that omni-potent clause, "The Bank’s decision in its sole and absolute discretion on all matters pertaining to the award or use of any or all of the benefits and privileges stated below shall be final and binding on a Cardmember." Such is the Bank's rubbish policy.