I've checked it and "always on" is the selected option. It's the default option, I think. I've opened an issue in TP-link support about this, they say they are trying to reproduce the scenario...

Region : Spain Model : TD-W8961ND Hardware Version : V3 Firmware Version : 3.0.0 Build 120524 Rel.05221 ISP : Movistar Hello there, I'm using this router since Christmas looking for a better optiong...