Model : TD-W8980

Hardware Version : V1

Firmware Version : V1_150514

ISP :

Hello guys, I'm experiencing something very interesting problem here. I used my device as a wireless router for almost 1 year with no problem. Today I connected my adsl to my home and wanted to switch back to adsl mode. I did go back to adsl mode with no problem, fillled the username / password and wifi security settings. But after a while when I'm surfing in web-gui of the device, I notice that the web-gui switches to W8960 (300Mbps) and even W8950 (150Mbps) afterwards. I don't know what is really going on, it just happens when I am surfing in the webgui but I guess it should not happen at all. Any helps or ideas what is causing this mess?

Thanks in advance.