I suspect you have some sort of JavaScript / jQuery plugin attempting to bind to the click event of your link for a couple of reasons...
1) Single click (left click) behaves differently than right click -> new tab. (And I suspect if you copy/paste the URL into a new tab it'll work fine).
2) The word undefined
shows up in JavaScript when you attempt to use a variable or call a function that is undefined.
I would inspect the console and see what errors might be reported.
If you don't have any errors in the console I would inspect the links themselves and look for any classes or wrappers that would indicate a plugin might be trying to target them.