-b/ or -c/ added to URL, Page not found, in some browsers

Dear all,

I have a problem on a WP installation that I’m unable to solve.

In Firefox 38.0.1 when I click on the word “hier” (Bold italic) on the page https://nemacademy.nl/opleidingen/ I’m directed to the page https://nemacademy.nl/opleidingen/movers-opleiding/. After a second, the URL is extended with ?utm_expid=68377794-0.u-WEWBKtQe-e4KR45RdkPw.0&utm_referrer=http%3A%2F%2Fnemacademy.nl%2Fopleidingen%2F But it still works: The page loads.

However, in Chrome 43.0.2357.81m I’m also initially directed to https://nemacademy.nl/opleidingen/movers-opleiding/. But then -b/?utm_expid=68377794-0.u-WEWBKtQe-e4KR45RdkPw.1&utm_referrer=http%3A%2F%2Fnemacademy.nl%2Fopleidingen%2F is added. And I suspect that it is because https://nemacademy.nl/opleidingen/movers-opleiding-b/ doesn’t exist, it doesn’t load. I get a 404 Page not found.

I also had reports of people being led to https://nemacademy.nl/opleidingen/movers-opleiding-c/?utm_expid=68377794-0.u-WEWBKtQe-e4KR45RdkPw.2&utm_referrer=http%3A%2F%2Fnemacademy.nl%2Fopleidingen%2F And I can confirm that that is the URL you get when in MSIE 11.0.19600.17801.

It makes no difference (in FF) whether one is logged in or not.

Now Firefox happens to be my preferred browser, ?? but I still need to solve the problem. Is there somebody out there that can help me out?

Thanks in advance, Thomas.