:judith-ziekte-van-crohn-draaglijker-dankzij-kefir&catid=2:getuigenissen&Itemid=36
Why is that in there? What is creating those links? It looks like a very poor attempt at an SEF-link builder Joomla extension to me, and the JoomlaComment component isn't injected.
Your HTML output on every article is broken, Acajoom News is crashing as breaking the PHP processing. Try disabling that extension, clearing your cache, and see if the Read More/Lees Meer buttons create the proper shorter links.
EDIT: Sorry, bo I don't think it's the Acajoom News module, and the HTML is not broken. It looks like it is broken because it has style="text-align:"> in the module which gives me an error (empty text-align style) but that's all.
I don't know why it's even creating those extra-long links, I'm pretty sure there's no option in Joomla core for it so I guess it's another extension. Maybe Daniel knows. If you would be willing to give me backend access, PM me a username and password to login and I could take a look? Or we will wait for Daniel, he might have seen this before