Looks like router is faulty

.in another router what i have is ping on wan okay, Looks like bug in firmware but I can't confirm for 100% because I don't have this router at home.

Your router W8951ND, right?

Previously master w8980n didn't need any wds settings to work perfectly with TL-WA850RE range extender. WA850RE it is typical repeater however. W8960N like W8980 are typical ADSL routers and radio...

Your main router is? Can you give us screen shot from your settings? W8980 and W8960N have different chipset and I think that is main problem in WDS configuration.

I think that is problem with "https" - (web secure protocol). I don't know a solution for it in original firmware.