The bug / warning has become worse with the latest iterations of Quicken desktop. Now the notice is popping up when I edit a split transaction. In the process of completing ONE check, the notice popped up 6 times. Twice while editing split, twice while first entering transaction and twice when saving.
Please Quicken, either give as an option to suppress this warning or nuke it entirely. It's really not necessary. I use the brackets on a fair number of memorized payees to organize the payment type (for example, GAS / ELECTRIC for utility).