What the others said.

Almost definitely a browser issue, or your settings within the browser.

Clear cache and cookies, reboot your device.

If that doesn't work, (or probably before but those things are handy to do regularly) check your settings.

There will be something like a default to open tab in a new window. Disable it if you don't want it.

Just checked mine and all is ok.

Have you cleared, cookies, cache, etc.  Sounds more like a chrome issue

I do not know if other members can help you

Is there something in your Chrome settings?

How do you know it is an eBay issue and not a Chrome issue? 

Does it do it in any other browser or any other website?